Hi Jellyhead,
My parents are divorced and both remarried and all four of them hate one another!!!! (especially the two mums)
Like ilonabryan, we are having 10 people on our top table but if either of them complain about anything, they will be demoted to a guest table!!!!
Don't know about you but i have had to consider everything from who i go dress shopping with, thankfully my mother didn't want any part of it which reduced the headache considerably. I even have to organise the order of which they all leave the church, there must always be people between them!!! It's a nightmare and one that we shouldn't have to deal with on our wedding but sometimes that's just not possible.
I really feel for you as i know how hard it can be. However, you are definitely not alone. Try to keep calm and deal with things bit by bit. I think your idea about the tables is a great idea and will solve a lot of stress on the day.
Good luck!!!

Beeny