My divorced parents can’t be civil for my son’s graduation

DEAR ABBY: My parents have been divorced for almost 30 years. My father is still furious with my mother, and she is indifferent toward him. 

My son is about to graduate from high school, and both grandparents want to attend the ceremony and dinner afterward.

However, Dad refuses to be in proximity, or even sight line, to my mom. He wants me to plan the day so there is no chance they will cross paths — separate cars, separate routes, separate seats, separate photos, separate meals at different restaurants.