MIL and baby daddy drama......Please HELP! Mostly about baby shower!?

Invite them out of courtesy. I think you should talk to your mother in law and sister in law and get to know the family. The drama might be due to his and your age difference, and will continue until they get to know you. There may be a story you don't know about the girls, especially if they've known each other so long. I'd be interested in why the husband doesn't want them in the same room. You can tell the mother in law they were invited, and that you hope there isn't a problem since they've always been good friends to you and you didn't know she and they didnt get along. It's your shower, and you'll probably just keep running into these situations until these people deal with whatever is bothering them. Best of Luck dear.