O.H.
You will get all kinds of advice and some opposite of another...from people and books. And example is this: My ex and I were required to take parenting classes in AZ BEFORE the divorce was final. The counselor said that it is HIGHLY suggested that you do NOT continue to hang out and do 'family' things together such as holidays and birthdays. It is hard enough on the kids living in 2 houses let alone on occasion seeing their mom and dad get together and have fun with them. He said the kids, no matter what age, will always want their parents back together and if they see you getting together and hanging out, it will make it look like that's a possibility when it isn't. So he actually said to have separate celebrations and not have them together to make it CLEAR that you are not getting back together. Continue to be civil but don't hug each other good bye or hello, it's misleading to the kids.
You didn't ask this but I'm saying it because the other person suggested it and just to show there is a lot of "opinions" out there. My advice is to maybe read a few books but really keep open communication with the kids and counseling would not hurt. I wish I had taken my kids. As awful as it is for you, it's a million times worse for them. I'm glad you are making an effort to help them. Good luck.