That is where the issue of seating comes into play.
Cheap Seats
Problem:: "My parents don't get along at all. I can't imagine seating them anywhere near each other durning the ceremony. What should I do?"
Solution:: At a typical wedding, the first few rows of seats are reserved for close family members, with parents in teh front row, grandparents and siblings in the second row, and so on. If the relationship between your parents is that tense, tradition wedding etuquette states that the parent to whom you feel the closest - let's say it's your mom- would sit in the front row, while your dad would sit in the thrid or fourth row (with your stepmother, if he has remarried).