How old is your son? It may be due to conversations with his fiancée that these names ended up on the list.
I agree, if the list is still being edited, ask him why. If it is a done deal, say nothing, let it go.
I had a similar experience where my son added the parents of some of his groomsmen to the his guest list. I did ask him why, and let him know this one couple was someone I would never have included.
He said he thought he was obligated to add them.
I let him know there was no such obligation.