I don't buy my stepson anything for his birthday, nor acknowledge it. If he ever starts acting respectfully toward me, I may change my mind on that, but I don't buy presents for people who treat me like rubbish and disrespect my home. I do allow my children to buy him presents, but I don't encourage it. I did end up attending his birthday party two years ago, but I had a friend come pick me up early because it was just really bad. I don't think I'll ever go to his birthday party again. The way I see it, we have no real obligation to honor these people's birthdays. Honestly, it is a sad day for me because his existence, which began with his birth, has not brought anything but hardship to my life and that of my family. Why would I celebrate that?

You can ignore the teen's birthday... but don't be surprised if your DH still takes his teen out for birthday dinner and he self purchases and gives her a gift.

Disengaging means you don't participate. Doesn't mean Dad won't do anything.

I'm sure you were disappointed the skids didn't acknowledge you. However it sounds like your DH did try. He invited your friends/family and had cake. 

Yes, his kids are disrespectful brats. I bet even though they ignored you they managed to bring their selves to eat some of your cake. 

Just let Dad worry about his children's birthdays. You do not have to participate, don't have to buy any gifts nor put out any cash towards any of it. 

Disengaging usually means (IMO) mentally disengaging and sometimes physically disengaging. Example, not giving a hoot if SD15 gets a party celebration or not, that it won't be hosted by you, no happy birthday wishes or card/gift from you nor will you pretend to GAF by going out to dinner with her.... but if Dad still takes her, so what. 

The definition of disengaging to me does not include forbidding her father ignore her birthday merely because she didn't tell you happy birthday on yours until forced to. Forbidding is not disengaging , it's attempting to control. 

If Dad makes plans to take SD15 out to dinner one evening, why not pick up the phone and invite a female friend to go elsewhere for dinner and drinks . Go enjoy a 'private' belated birthday. No husband. No skids. 

Ignore the whore.

Because you have a supportive husband, I could see celebrating with SD to keep trying to get to a better place with the skids. It's when you don't have any support that disengagement is the only option.

However, if you're done with them and you're really disengaging, you can't expect a "Happy Birthday" from them and you don't have to offer them one.

Given that they begrudgingly offered you one even though forced, I'd feel obligated to participate to some degree, even if only wishing them a happy birthday (or they can throw it in your face that they had to do it for you and a short time later, you didn't do it for them).

Next year is another year when you can expect nothing, get nothing, and then give nothing. But this year, it might be best to at least say it just so you show them you're giving exactly what you're getting back from them.

one expect something next year,  They know it was her birthday and did not wish her happy birthday.  No matter what you do. Nothing is going to change.  I would go out to dinner, make DH make the plans, pick the restaurant paid for it.  I would order a good drink or two or three and the most expensive thing on the menu.  App, and main. I would not wish kids a happy birthday. A kid talk about subject kids have no interest in. 

Disengaging to me means doing what you are comfortable with.  I don't see it as a one-size-fits-all, as each situation can vary.  I'd look at it as more as happening on a series of levels.  Maybe, level one being just not going with DH to every event (despite him wanting you to), but still remembering and including SKs in special events in some way.  All the way up to level ten, meaning you have absolutely nothing to do with them whatsoever, and DH gets to see them elsewhere if he so chooses.

Some SKs are just fine, some are OK, some are snotty, and some are just all out hell.  The point is, not all SKs deserve the same level of disengagement.  It is not a tit-for-tat thing, as much as it is a way to get DH to deal with issues with his children that are really HIS issues, and a way to give you some peace and save an otherwise unfairingly stressful marriage.  So, the key is to go with what YOU feel comforable with and what YOU feel you can live with.  So, if you want to avoid SKs' B-days for one year to see if they get the message, try it.  I guess I'd add you have to look at what is the message you are trying to send/ get across vs. being tit-for-tat.  Or, if you are just trying to protect yourself and save yourself some peace, that is OK too.

I think for younger children, the focus should be more on trying to send a message or teach a lesson, if you want to call it that. Or, just simply letting the kids know that their dad has to be their dad.  You are not going to play that role for him/ them.  They may catch on.  However, once the children are older, are adults and have shown a pattern of a lack of respect and cruelty toward you, then it becomes more a question of saving your marriage and saving yourself some peace via disengaging.  DH gets to deal with it.  As everyone is always telling SMs, they are his children (even as adults) and not yours.

I am never in charge of skid birthdays. I just go with whatever DH plans. I pitch in for a gift but it’s something utilitarian like a notebook for school. I wait until later in the day to mention happy birthday in a quiet nonchalant half ass way then continue what I’m doing. 

DH makes the skids wish me a happy birthday but if they didn’t I wouldn’t give a crap. They don’t hold that much power over my feelings.