Wow, that's impressive of your dad to not give up. For most schizophrenics, they become alienated from their families.
Sometimes schizophrenics are truly brilliant. Mom retained a public library card when we were on the streets and we went to the library almost every day. The librarians were wonderful and chatted mom up about what she was reading and how she liked yesterday's books.
The astonishing thing is she would get 7 books at a time (the limit), one for me. I'd typically pick something like the biography of Wild Bill Hickok and it would take me 3 days to read it. She would read her 6 books in a day or two. I would say "Mom, how is that possible? No one can do that." And I'd open a book and ask her about some stuff I could see in it. She could answer correctly. I never figured that out.
At Stanford, they had a speed-reading class based on Evelyn Wood and I took it because I wanted to be like mom. I failed at it and Stanford discontinued the course, saying it reduced comprehension.
Mom claimed to have memorized the complete works of Shakespeare. I was never able to verify that because I hate Shakespeare. However, when I tried to read Hamlet, I recognized what I read from the things she'd recite as we walked.
If you want a fantastic read on how brilliant they can be, Simon Winchester's book The Professor and the Madman is riveting.