J.C.
Is he able to write? How is his speech? If he can do either one, he can take up the hobby of writing a "Memory Book" for his children and grandchildren. He can put together a book of memories of his life, words of advice, places he traveled to, etc. Your mom could help him, if that is the case. They could even combine their memories into one book! I know that I would like to start putting together a book for my children and I really wish that I had known more about my grandparents pasts.
I am not sure if you were looking for an income producing idea or not, but the only thing I could think of was something that would benefit the community. What was his profession prior to the strokes? Can he train individuals in that line of work from home? Did he excel in any one subject in school? If so, he could tutor less fortunate children for a low payment. Do you have the funds to purchase t-shirt making equipment and have him start his own business making t-shirts, bags, etc? I know that there are smaller machines for smaller budgets and you probably can find them on Craigslist or Ebay. I thought of that one because my father-in-law has a t-shirt company and one of his employees had a stroke and was still able to work. I am not sure if these are hobbies or not and I wasn't sure if you needed income producing ideas, but let me know because I have a book with a ton of ideas for starting a business from home.