Almost everyone goes through something like this; it's hard but it's part of life.

You say about your grandfather "Had he not been cremated, he would be rolling over in his grave." but he probably wouldn't.

The older you get, the more you see that this is life. It may not be the life he knew, with multi-generations in one place but he would have acknowledged the need to change.

You can't expect your parents to stay in that place to preserve everyone's memories.