You don't disengage to punish anyone, you disengage for yourself. You do it to save your sanity. You do it to keep from getting hurt. Except for the part about him inviting them to your house without your knowledge, didn't your life get better when you quit having to deal with his family?

disengaging, while about them, is mostly about you. you do it to protect yourself, you do it to not be a doormat, you do it for you. 

I will say that disengaing does not make you a horrible person. I can understand how that can feel that way, believe me. Especially when you get negative reactions from those you Had to step away from intiially trying to make you feel that way , as if your decision was made just for the purpose of Punishing them or treating them badly.  Anyone who wants to give you grief or suggest that you are "selfish" or heartless as if you should feel guilty, ( which has been my experience) because you stood up for yourself doesnt belong in your life as much as you can help it. No one should seriously expect you to revert to being unhappy or a good natured doormat for THEIR comfort! No more!  As another poster asked...think about how much peaceful or happier your life is for not putting up with certain people?  If you be honest with yourself and come to that conculsion, then Id say you are doing the right thing. Same when said people get that offended over you setting some limits,  since that tells you thats the kind that you need to keep distance from so you make the correct choice. 

Being disrespected by there family.  How do you define disrespect.  Showing late for holiday dinners.  Boyfriends family dysfunction is valued over you [ Disrespect].  Liking the ex more [ Disrespect]. Not makeing you feel welcome at wedding, funeral. [ Disrespect]   
ACTUALLY DH going to see SD without you is also disrespectful to you.  Guest that where they learn it from.  You are in a no win situation.  

"Since he chose to protect his daughter from me for about 6 months, even while living together (I left if she came over)."

Did he ask you to leave when she came over so as to keep you apart? Then he wonders why you aren't accepted as his wife?

"Then, his oldest sister took the opportunity every time I saw her to tell me I need to love and take good care of her brother (my husband) because he's a special person who the whole family cherishes. Little do they know he has been a liar, cheater and pos to me throughout our relationship."

He has been a liar and cheater throughout your relationship? He sounds like a narcissist. No telling what he tells his family about you behind your back. Narcs like to triangulate. 

 Little do they know he has been a liar, cheater and pos to me throughout our relationship. 

I'm sorry.. but this statement?  If this is the case..why on earth do you stay with him.

His family isn't the problem.. HE is.  

I've been disengaged from my DH's kids and family for over a year now (after 12 years of peace and happiness, or so I thought, as a blended family). In my case, DH disengaged with me. He has virtually no contact with his kids and mother, and zero contact with the rest of his family. Talk about feeling like a horrible person. The thing is, we only get one life to live, and I wasn't going to spend mine being married to half a person. When things hit the fan with DH's family (I won't go into all of the messy details, but it's all in my blog if you're interested), I would have completely understood if DH couldn't separate from them. I would have been heartbroken, but I would never have blamed him. At the end of the day, I refuse to leave space in my life for people who treat me badly. And I refuse to be married to someone who leaves space in their life for people who treat me badly. I'd rather be on my own than be married to someone who doesn't put me first. So he had to make a choice. And he did. And when I feel like a terrible person, I remind myself of that. HIS family put him in a terrible position. And HE had to make a choice between them and me. It's about their crappy conditional family relationships, not mine. 

Him playing both sides doesn't help anyone except him .   He getting what he wants but nobody else is getting anything.  When he entered a relationship with you,  He knew how his DD was. 6 month to meet you. Where did SD think her father was living?  
'wasn't going to be happy about this.  But he choose to be with you.  Now he's playing games.  He made his choice he must back you. He's living with you. He must show you the respect you deserve.  

What you are living is exactly why I do not support disengagement. My stand is just the opposite. Total confrontation of toxicity immediately upon them bringing that toxicity forward.  Requiring that our mate is our mate above all else that they may be, and clear that the marriage  is the sole top priority. Anyone else has standing based on what they earn with reasonable behavior and decency. If they are not reasonable and decent, they are written off and must face the full facts regarding their crap, and every legal, financial, and social consequence possible.

If the mate is not of sufficient character to stand at our side, they are write off a well.

IMHO of course.

No tolerance, total confrontation bringing every fact, legal weapon, financial weapon, and social weapon to bear resolves this kind of crap in short order.  But only for as long as zero tolerance is practiced with extreme prejudice.  Rather than tolerating their delusion on the "quality" of your chating abusive, neglectful DH, give his family the unadulterated facts.

I also do not tolerate sneaky void of character manipulative bullshit from anyone in the blended family mix regardless of who they may be. I would not tolerate it from my mate anymore than I would tolerate it from anyone else in the blended family mix regarless of who they may be.  

Abandoning our place as equity life partner with out mate, tolerating them abandoning their place at our side, sniffing the asses of their toxic failed family progeny, sniffing the asses of their toxic family (our ILs), etc... I learned these lessons in my first marriage.  My XW was a serial cheater, my XMIL was an eventually convicted federal felon, and I escaped before I was sucked fully into their toxic characterless family bullshit.  I also blessedly did not sully my gene pool with my XW.

I've been pondering on this post for a bit...for me I don't see disengagement as a double edged sword. For me disengagement brought peace, respect for myself and happiness. Before disengagement I was NOT treated like an equal family member, I was not considered - my feelings never mattered, constantly criticized and expected to do all the crappy stuff with no benefits. I was also always held responsible for everything wrong - no one else in the family viewed their behaviors and were responsible. When I look back I wasn't losing much if anything at all. It was very SCARY to do it at first but after a few more rejections and horrible behavior I got the message clearly that you want to show me and the world "I am not family." Why would I want to be subjected to that over and over again? Many of us feel the same way. 

Your test should be: If they treat a perfect stranger better than you what exactly are you missing out on? 

These days I am happy to see their lives move on and I take no interest in what's going on. I have a fullfilling life and I have redirected my energy. Take a look at what's going on and evaluate whether this has been good, fair or even beneficial to you. I bet my money that it has not.

I've moved past the anger I felt about disengaging. Now it's resentment (toward DH) but even that's rare. I too spent holidays running around to please him and his kids when all that got me was excluded. I was not welcome in their little world. DH would never do holiday things with me (Christmas concerts, plays, etc.) because they made him "too sad" without his kids. But the ONE year they came to visit us he pulled out all the stops. "For the grandchildren."

it's rarely an issue now since SD isn't speaking to him. And SS hasn't been to our house in ten years or more. DH can no longer travel by himself and since I won't go to see his kids, he's out of luck.

Oh well. I have no regrets. I'm sorry DH gets sad about it but I didn't create the mess and I can't clean up the mess. 

With out knowing what we are doing. No one unless they lived it can't understand it.  And many of us who lived it can't fully understand it after many years of dysfunction.  I believe that someone who divorced with kids ,  there something wrong with them to break up there family over there wants. .  
'If the SO was good enough to have kids with, there are good enough to stay until the kids are older,  and develop to adults 

SP have a major problem fitting in.  You disengaging, was a safety  mechanism, to make your life function.  We pay the bills . Clean, cook, and don't  like to be disrespected .  We don't run a flop house. Our SO are so guilty that they take crap and kiss there kids a$$.   Because they know the happy family they wanted is gone. Forever.

You did what you had to do to survive.  At this point there nothing you can do. You will continue to live your life the way you haved.  It's not your fault.  You didn't divorce, and then started a new relationship you could not handle. 

We do this to protect ourselves from dysfunctionaism of Steplife.  To maintain our mentally  sanity in life.  We will not alow other people to run us in circle's.  Not to give of ourselves and our money and tine to be disrespected. Time and time again 

As bad as disengagement is its better then being used .

I would not tolerate a partner who backed me into such a tight corner with their hell spawned failed parenting, failed family progeny, failed adulthood, failure to engage in the relationship, and failure to protect their mate and marriage to the level that forced me to disengage.  If they are that much of a failure in their lives........ 

Good riddance to the source along with the product.

No one with this kind of baggage is not responsible for that situation.  They are responsible for it either in whole or in part. At some level

Either way, not worthy of being my partner, or anyone elses for that matter.  If they do not step up and solve the problem, then I can solve in in my life instantly and permanently.  I cannot rescue them or their kids. It is not my responsibility.  It is theirs.

IMHO of course.

It most likely not effect the person/ persons your disengaging from.  These are people who you will never be friends with in the real world.  You have the satisfaction of not helping that person you are disengaging from.  You are not cooking, cleaning, taking them places, giving them gifts and money.  
IF your SO doesn't understand and makes it them against you,  you will be lonely.   But you do have time to make new friends get new roads to go down.   Volunteer for a good group. Food bank.  Free meals group. Where good people volunteer.   Once you start ant network you can find places you really enjoy beaning at.  With good people.  Getting away from all the toxic dysfunctional family