I want to ask my wife to not allow my FIL in the delivery room
Why do you think that he should not be in the room?
She's going to have a difficult delivery and I don't want him in the delivery room.
I think that this is going to be a stressful day for your wife. I think that you should not tell her who can be around her, especially on a day as nerve wracking as delivery day.
I think I'm going to tell her that she can't have her father in the delivery room. She will just have to follow my decision.
She carried the baby for nine months and she's the one giving birth. She can have her astrologer and aromatherapist in the room if she so chooses. The decision on who's allowed is up to her and her doctors and no one else.