My 76 yr old father had open heart surgery a few weeks ago.?

He normally lives with my 78 yr old mother in their apartment, but he has been staying with my wife, 2 children (3 & 6) for the last 2 1/2 weeks. He has recovered well, but I am already burned out. He can care for himself now, but has not mentioned returning home. My wife and I are simply too tired with work and kids. My mother is somewhat selfish and has not exactly volunteered to take over at their home. How do I bring up the subject of him returning home without hurting him?