Wow, I'm happy to hear that your Dad's shown improvement! Its wonderful of your sister to move back, she will have nothing to regret having done it. I'm sure it is really good for your Dad and also the rest of the family. Everyone knows he's in good hands and can worry a little less. I hope, of course, that he continues to baffle the doctors!
I saw my uncle Joe 2 weeks ago. He has lung cancer and did well for a long time but has been declining. His daughter has been taking care of him on weekends for the year he's been sick. She lives in upstate NY and drives 5 hours to come down to take care of him on the Cape. He loves it, it's been really good for him. She's helped him alot with the nausea, she is a doctor and very intuitive so came up with creative ways to help him. I think they've both benefitted alot from her care.