I'm thinking of telling my mother that my future son will never be allowed at her house
Why alienate your son from his grandparents?
It's because he will be better than everyone in my family
That is being a bit too hard-headed. Preventing grandparents and grandchildren from interacting is wrong.
That makes sense, I'll rethink this.
It is good you are looking out for your son and I'm sure that they will get along with their grandparents. You'll all be happier as a family if you work out your problems together.