you can't white knight for your ex anymore, let her figure out household stuff.
In terms of the other children, keep a relationship with them that you would like. They are old enough to make their own decisions and pretty soon will be legal adults. What is your ex going to do? control their behavior? Keep it positive towards them, make them feel welcome and chart a course for the type of relationship you would like with them moving forward.
Or not, up to you, but don't feel, with their age, that they can't or shouldn't be able to leverage their own critical thinking skills.
Keep your head up, one day at a time and keep your focus inward - yourself, your life, your child. You no longer have to concern yourself with your ex, which is a good thing, remember?