I agree with the others, you need to talk with a CPA, but you also need to talk with a mortgage professional to get pre-approved for a loan.
If your father is not going to use a real estate agent. He should have an attorney look over the paperwork and should still do all the disclosures.
We have all heard the horror stories over the years of problems when families or friends buy and sell homes to each other, for whatever reasons. You should also get a pest and home inspection to protect all the parties involved.