1) Go slow; there’s no easy win and it’ll take time for things to smooth over.
2) Encourage mutual respect with your ex’s. Do your best not to argue, get snippy or fight in front of the kids. Encourage your new spouse to be pleasant to your ex as well.
3) Involve your kids in big decisions with your spouse, i.e. engagement and wedding plans, vacations, etc.
4) Mutually agree on punishments
5) Make time for just you and your kids, for example without step-mom or step siblings.
6) Create a personal relationship between you and your spouses kids. Find common interests, i.e. movies you both like, sports, shopping, etc.
7) Get some counseling early on.
8) When you're all ready, take a trip together; make experiences that the kids will remember.
9) Have the kids help each other with homework.
10) Show your kids (and her kids) how much you love her. Be affectionate but not over the top.