K.M.
Hi W.! Are we related? :) My husband's family drama looks good from 3000. His parents too have been divorced more than 25 years, yet there is still a great deal of bitterness. When we go home to visit we make it a point to set a schedule so that we see both sides of his family and his sister can see us whenever she chooses - with both his mom and dad.
Now that we have a child, my husband makes the effort to visit, but he has told him mother she needs to see someone if she is not over the divorce - since then, she doesn't say much. Neither of us engage in conversations with his mother or sister regarding his father or step mom.
No one really speaks to me regarding the drama because they know I will put them in their place - especially since I want my daughter to know them all, but I will not tolerate them saying anything negative in front of her.
Try being frank and telling them to grow up and move on, or you are done with them. Also, is your husband supportive - make sure he stands up for you and to them. It is important that your two children have the benefits of both of their father's parents, so remind them what is at stake - they must behave and be polite to maintain a good relationship with the grandchildren/niece and nephew.
It is so unfortunate that we - the outsiders have to deal with drama that occurred long before our entrance, but such is our draw. Good luck and feel free to email me if you need to vent. Honestly, reading your request reminded me so much of our situation, we are just further away, so the excuses for not visiting are easier!
K.