You bring up a wonderful point about schizophrenia, not that schizophrenia is wonderful, although I would suspect that there can be somewhat of a positive schizophrenia, although it wouldn't be called that at all.
Blind and deaf people can hallucinate, the blind can see, and the deaf can hear, what an odd sort've coincidence that one is.
Look it up, if you do you will see this can happen.
Possibly at such an age, your Dad is suffering from some form of dementia, sorry to say. Possibly Alzheimer's - for which medication to slow or halt the condition (it it is this) can be given, but these will not make him recover his former self. Just prevent him deteriorating further.
I wish I knew more and could help you enough on this. However, your GP can do blood and other tests, and arrange for other caring help. Also, your local council can give monetary help for a paid carer, and other needs. This is often known as In/Direct Payments. If you go into the webiste of your local council and key in In/Direct payments there should be info. If the website of your own council is not clear enough, try the website of another council, just to get a clearer idea of what is offered.
Some councils may term it as 'Independent Living Allowance.
However, the bookkeeping for your Dads spending would have to be very accurate, with receipts. If the council thought the money were beings misspent they would claim the money back, so it is imperative to use it as agreed, and if anything else is needed (mobility aids, for instance) then you would have to approach them again.
In any case, the GP should be the first port of call and if he/she isn't of much help, see another GP and insist on your Dad being referred to s Specialist.