If these are adult Skids, I don't know that disengaging is possible either. They have their own lives. I think you may just need to stand your ground and demand respect. If your DH wants you along when he goes to visit his kids, then you have EVERY right to go along. I would kill them with kindness, show them that you can be respectful even if they can't. Eventually it may or may not work, but as your DH's wife, you shouldn't be excluded. DH may need to step in too.

I can tell you from experience that disengaging applies only when they are in your house. When the older SD moved in with us a few years ago at age 21, I simply stopped doing things for her when it became apparent that she saw me as a maid. Now that she has moved out and lives 5 minutes from our house, I don't have that option. When DH invites her over, or she drops in with our grandson, I can't really just ignore her. Same thing if she ends up going somewhere with us. I have simply come to accept and expect that she will talk mainly to her dad, often waiting until I leave the room to tell him anything. DH will never see this, even though I have pointed it out to him. If your DH is not inviting you to the dinners, etc, you should definitely tell him that he is way out of line, but don't expect an apology. He may be doing it because he sees the tension between you and the SKs and he thinks he is "helping" you. The SKs probably won't apologize for their bad behavior either.

I guess what I am trying to say is that you can't feel hurt if you just accept that you mean nothing to them. I don't like my SD and I have reached the point where I am GLAD she ignores me.