I don't know the back story, but that is a lot of people from your family and his that seem to be concerned.  If you can set aside the feeling of being judged for a moment and just look at what the concerns are, you may find some harsh realities and red flags.  I definitely wouldn't get married until you feel better about those red flags.  No harm in waiting.

It's not necessarily that you should be with someone who doesn't have kids, more like not all men with kids should be in a relationship, and this guy may not be right for you.

If your SO feels that his kids will always trump what you want, there is going to be a lot of resentment. From your other post, it doesn't seem like the two of you are communicating very well about this issue.

Also, for him to get mad because you wanted to do your own thing when he wanted to get his kids, is unacceptable. HE has kids, they are not yours, and you are not obligated to spend all of your time with them.

You DO need a different therapist. "Well, you're marrying a man with kids," just doesn't cut it, is not helpful, and is not going to solve anything.

Frankly, if your SO doesn't want to take your feelings, needs, or wants into consideration, if he cannot balance being a divorced father with being in a relationship, HE is the one who should not be in a relationship. Then, he can focus on his kids and not have to concern himself with being somebody's partner.

ETA: Don't think of it as everybody judging YOU, they are seeing a situation that is not working, whether it be due to you, due to your SO, the kids, whatever, it's not working. I'm sure that your sister wants the best for you, maybe she feels that this guy is not it.

One thing that you do need to remember.. your husband to be is a father "full time"... even if his custody schedule may be part time.  Also, at any moment, his part time custody could become full time.  His Ex could die, go crazy.. go to prison.  You just can't absolutely count on him only having his kids on his "time".  He is the kids' father and it sounds like he is interested and happy to have them over any time it is possible. 

Now, in your defense, does this mean that YOU need to take care of his kids? NO.  Does this mean you have to clear your schedule to play candyland when you really just wanted to relax and take a hot bath?  NO again.

His kids are his responsibility.  Now, it seems you have to date kind of "played the part" and set the expectation that you will hang out with him and his kids...   In reality, it may have been a little easier if you had just from the start set the expectation that his kids.. his entertainment.. and that you would sometimes rather do your own thing..

When he wants to have his kids over to his home (even one that you are sharing).. it is not exactly the same thing as him inviting his poker buddies over to drink beer.  These are his kids.. his family.. and he is naturally going to feel like his kids are welcome in his home "any time".  Now, that doesn't mean you have to be present.  But, I think he got the impression that you going out that time was you kind of trying to get back at him.. or that you were just making excuses because you didn't like his kids.. "ooh.. I'm tired"'.. o that didn't work" I'm going out"   If you said.. "honey, I'm pretty tired tonight.. if the kids come over, i'm probably just going to take a bath, do a little reading in bed and hit the hay early".  It might not have come across like you saying "i want control over when your children are here".. it is more "please respect my feelings" which didn't prevent him from having the kids.. but put him on notice that he needed to make sure you weren't disturbed... which I think is more within your rights than barring his kids from the home.

I find that most people who have not been stepmothers (and maybe even some who have) judge stepmothers. In my view, this is driven primarily by societal conventions about what a "real family" is. I think that in general, people don't feel comfortable when families break up, so even if the stepmother wasn't involved in the break up, she is seen as the interloper, the one keeping the original family from maintaining all of it's traditions, etc. 

Also, regardless of the circumstances of the break up, in general, mothers are viewed as the victims of divorce, especially if they have full custody, and fathers are viewed as the deadbeats who are leaving the mother high and dry. Therefore, anyone associated with the father is often viewed negatively, because he is seen as not giving enough to his children post-divorce as it is, so if he's now giving anything to another woman, that makes things even worse. Also, many mothers use their children as a bargaining chip to retain power over the man they divorced after the divorce. This often leads to blurred boundaries. 

Also, family members often feel the need to step in and save the children, seeing them as the victims of the divorce. In reality, if everyone just calmed down a bit and let things play out and let everyone accept the new normal things would be okay. Is it ideal for children to have parents living in two separate households? No. Is it better for children to have parents living in two separate, but happy households, as opposed to one household where there is anger and chaos? Hell, yes! People often seem to forget that even if mom and dad stayed married, that doesn't mean it would be a good situation for the children. I would venture to guess that growing up in a household where there is abuse or constant fighting is more damaging to children than divorce, but people rarely admit to abuse and fighting in a marriage, so that is difficult to study. 

All that being said, being a stepmother is difficult. Your life is not fully your own and you need to accept that. You need to accept your new normal. However, I think you should be allowed to express your frustration and your SO needs to be understanding. This is his situation to own, not your situation to take on. 

Finally, your sister was way out of line for saying that to your fiance. If you shared your feelings with her, she should not have shared them with your fiance. That is betrayal in my book and you should have a serious chat with her. If that is how your family operates, my advice is to seek personal counseling to figure out how to step out of that dysfunction, because it will only make your life hell if you can't even count on your own family to support you through what will be a bumpy transition to steplife (a transition that could take 5-10 years). 

Yeah, I'd agree with the others that I don't think it's necessarily *judgement*, but I think most people (including ourselves) are aware that being a stepmother is going to be inherently harder than being in a "regular" relationship. Anyone who hasn't been in a stepmom's shoes doesn't know exactly what it's like. Similarly, anyone who is child-free doesn't know what it's like to be a parent either, but we still know it's hard. Our friends/families know stepparenting has a reputation for being difficult, we then verify that with our stories and venting, so it's probably natural for them to wonder why we'd want to pursue it. Biomoms can complain about parenting, but no one's gonna tell them "well you shouldn't have kids then!" It's such a double standard.

It sounds to me that they may be right but for the wrong reason.  They appear to believe that the problem is you not wanting to be "insta-mommy" and sacrifice yourself and your time for the children he created.  I think it is more accurate that the problem is that he seems to believe that the children he created are your responsibility rather than your choice.  The people in your life have likely accurately seen that the two of you are not a great match at the moment.  They just have swallowed the society party-line that anyone with a vagina is supposed to take care of any random kid put in front of them and so are putting the fault at your feet rather than at his.

If you generally enjoy this relationship, maybe try and find people to vent to that aren’t family. I’m sure we have all done it, and it appears that if we vent to them it invites them to give an opinion. I am judged as a step parent and bio parent. And try to let it wash over me now, as I’m not perfect but I try to do my best and that’s all I can do.