I really get what you are saying but if you were to move within one hour of parents, would you really believe they have a right to an opinion about it?
I certainly wouldn't.
Now being their only support is something for their child to navigate.
I have several friends that have strictly not been in any way involved.
They had helped their own parents on their own and juggled children and it was made perfectly clear to their husbands that they would do the same or they would have huge problems.
It was their husbands golf time that took the hit, and their socialising, not family time.
But in a case where they bought the house right next door and said it was a surprise after the event, it caused ructions.
It nearly took divorce for it to be resolved
I hope the OP gets from this thread to tread very carefully and think about who she will be calling on for support.
It cannot only be her son as that will cause issues.
Perhaps teasing these things out before telling her son and wife is the way to go.
I still think one hour away is substantial.
OP should also look at nursing homes in the locality of her move.
Thinking ahead is the wise thing to do.
It is perfectly reasonable for OPs son to want to see his parents regularly if his wife sees hers.
Her worries about her parents feeling pushed out if her husband and children see his side is for her to navigate.
It strikes me as a tad controlling for her to think she has a say in him seeing his family if she sees hers very regularly.