What the others have said is correct. It's just a matter filling out a contract between buyer and seller and arranging the funding. There are a couple of things you have to look for though.
If you are working with a mortgage broker or banker, make sure they don't have a problem with the buyer and seller being relatives, most don't but some do.
Secondly, you will have to make sure the father isn't behind on any payments, if he is, the lender will more than likely shut the deal down in fear of him trying to avoid losing the house by selling it to a relative. This was very common strategy to avoid foreclosure.
I am a loan officer in Atlanta so if you want to speak deeper on this, PM your contact information.
Good luck