I wonder about the "feeding the son" - is that a special needs case? Or wont the grandparents eat with him? A 8 year old child should be able to eat and sleep at the Grandparents without much supervision, or being put to bed. Usually Grandparents like that and children also have to learn. And living 5-10 minutes away from the parents and doing the round trip once a day does not sound like "constant running around". And the old room in the parents home is usually not property, and parents are entitled to use that space when the nest is empty.