How do I get my grandfather to walk and take his pills?

My mother and I take care of my grandfather on our own. Basically he's gotten drastically worse in the last two years because he mostly sat in his chair and only ever got up to go to the bathroom, to the kichen, or to bed. Since he stopped taking his pills on a regular basis, he's been in the nursing home twice. One time for four weeks and the second for two weeks. He made the effort to walk at the nursing homes, but every time he would come back home he wouldn't try for us. We even had Home Healthcare come and help him with walking exercises and he would do it for them. But, when it was just my mother and myself he would claim that he didn't how. This is causing great stress for us both.We don't know how to get him to take his pills or practice walking. He sits in his wheelchair mostly the whole day., except when we get him ready for morning and bedtime and that's wneh he uses his walker. But he only uses it to take a few steps. We even tried having him walk with the walker, but he gets tired after going across the room once. And tonight after we changed him for bed , he couldn't even make it to the bed(which was a feet away) and he fell to the floor. It took us half an hour to get him up on the bed. I don't mean blame him because he also has demntia, but it's physically and mentally tiring trying to get him to do things and then he won't do them.