yeah i know how you feel. I didnt invited my parent on my wedding day, because i really hate them. but i was pressed to invite them. i put my foot on the floor and refused. Ok maybe in your case you dont have that option. Invite them both, and tell them specifically that the other will be there and that if they are not able to be in the same room for your wedding, that you prefer that they dont come. Your fiancée didnt force them to be there, she's just asking you to invite them...
after that if they dont come it will be there own trouble. And if they do came, put somebody near each of them to be sure that they will not cause troubles...
after that if they dont come it will be there own trouble. And if they do came, put somebody near each of them to be sure that they will not cause troubles...