FIL lives with us but is to the point that he just sits in chair all day. Is there any help?

He has mild dementia and depression. After colon cancer and a colostomy, we started co-living with my father-in-law to help him. That was 3-4 years ago... Since that time, he has had a reversal of the colostomy, back surgery, facing another back surgery, cataract removal, and the list goes on. My concern is that he just sits all the time. He does nothing to help himself and I have exhausted every effort to get him moving. We have addressed depression and he is in a two day a week program for that and it hasn't done anything. They tested him for dementia with a small test and it did show he suffers from the onset of dementia. He refuses to do anything at all around the house. I feel like his maid - all he is doing is existing. This can't be a good thing. I am totally frustrated. His day consists of making his bed, smoking outside, making coffee for himself and sitting in front of the tv. He drives to get his mail from the post office and out to the cemetery daily to pay respect to his wife that passed away more than 5 years ago. And he should not even be driving! I am not kidding when I say that is all he does. He's thin, looks bad and has absolutely no hobbies to keep him active (and doesn't want any). I am at a loss.... At this point, I feel it would be better if he was in a home where he was getting physical therapy to get him up; activities to keep him entertained; people to be around and someone else to cook and clean after him. But I don't know what direction to go.... :( Looking for advice.... I am not trying to sound mean, I just am fed up with the situation and exhausted.