As others here have suggested, get as much outside help as you can. I'll give you my story, the short version. Father-in-law lived close then moved north because mother-in-law had altimezers and he thought it would help her being in the mountains. MIL's brother lived with them since they were married 50+ years as he suffered from the rath of polio as a child. No other family members stepped up to the plate except on a rare occasion. Within 5 months FIL diagnosed with terminal illness and few options. Still no help. The straw that broke the camel's back was phone call from FIL saying he was getting the snow out of the gutters on the house because grandson was to busy to help. My husband took what he thought was an unpaid leave of absence from work and left immediately. Dad died six months later, and with deep saddness we put mom and uncle in nursing home. My husband came home to no job. We struggled income wise for a long time but, we would not change a thing we did.
I do have a suggestion. Get a tape recorder and do an oral interview of your dad. Ask directed questions about his childhood, what was his house like, inventions that amazed him, etc. This was done for my mom and I cherish it.