Family Relationships

Now that I am seperated, my ex's family is trying to contact me via email and other avenues to inquire about the children. In my head I'm thinking, what do you want? but in my heart, I know that my kids deserve to be apart of both sides of their family even though our relationship did not work out. It's very difficult to go over their houses to spend time with them in this murky situation. I'd rather not deal with it at all, but I know time is marching by and the kids are losing moments with their other grandparents and cousins. It's strange because some people in his family have really treated me bad and others have not. I wonder should I visit the ones who are staying neutral until this situation is all resolved? The kids don't notice a difference since they didn't really visit them anyway. Since my son was diagnosed with autism, they didn't really watch him or spend time with him. I always stayed with him in case he would get to hyper or to calm him down. It's been difficult, but I've tried to stay in contact with them and away from them at the same time. Any thoughts?