How to seat ex partners at a wedding!

I can understand not wanting to split up the friendship group but it shouldn't be a huge issue - people are still going to be able to talk to each other after the meal, and if they are such good friends, they will presumably be meeting up at other times anyway. So I think splitting the group would be the easiest way forward.

I would put one half of each 'ex couple' on separate tables - ideally with their backs to their former partners so they are not in each other's eyeline! and split the rest of the friendship group between those two tables. It's obviously going to be hard on the couple who don't get on to be stuck on the same table as each other, but if you split them up and leave the rest of the group together, they are likely to feel very hurt, so I think splitting up the whole group is kindest.