My best advice is to remember that it is your daughter's or son's wedding. For one day you can put your differences away. Maybe you will have a restraining order that prevents the whole upset from happening.
The one thing, Danielle, my daughter did was put her foot down. She did not want arranged seats and so it leaves the burden on where to sit on the guests.
There is also wedding pictures, traditions like candle lighting and the such which can make for a bumpy ride but just remember it is only one day. If the bride and groom don't want significant others in their parent wedding pictures than should be handled that before the wedding. Somebody's feelings will be pinged but the hurt will be carried on outside of your reception.
Kisses,
Deborah Stilettos
www.Facebook.com/MyDaughterIsGettingMarried