What do i do about family

They need to put their differences aside for you. Whether or not they like each other and with all the other guests they should be able to handle one night at the same event for someone they love. For the stuff leading up to it, if they can't behave then they don't participate. It's sad that that's what it might be, but they are adults and should act like it for their daughter. If anything they will hurt your feelings more than you are hurting theirs; for having to tell them to act appropriately or leave. Hope everything works out though and they surprise you by doing the right thing.

Agreed with the above comment - give them a head's up, and make sure they know you're serious about not tolerating unnecessary drama. They're adults, and they should be able to handle themselves, but I get that things happen. Otherwise, I'd just try to keep everybody separate anytime you can - different tables at the reception, far apart during the rehearsal dinner, etc. Good luck!

How about asking them to act like adults for one day so their daughter can have a drama-free wedding?

They don't like each other? Fine. But this day is not about them. It's about you and your FH. I would make it clear that you won't hesitate to ask any or all of them to leave if they can't act like adults and put their differences aside for one day.

I really think they will spend the time pretending they do not know each other. Do not seat them together. Try to be fair about whose names go on invites, how many guests they get, etc.

Sit the couples down separately and tell them what your expectations for them are. Also tell them something like "This is one of the happiest times of my life. Please do not bring past disagreements with {other couple} into our day. Please, just set these things aside for these days. I love and trust you enough to do this for me." This makes your expectations clear and in my opinion, pulls on the heartstrings. They don't want to be the ones responsible for ruining your day. I hope it all works out!