Can one be penalized for buying a home and selling it a few months later?

I ask this because my father is buying a home since my credit isnt all that great. I will live there and I will make the payments. In about 3 to 5 months I plan to buy the home from my father. I have planned to have the funds to buy it then. I was told that he needs to have the loan under the mortgage for at least 6 months and if not, he will get penalized. I sell insurance and have a few customers who buy home insurance for a home or two with a mortgage and then sell the homes within 3 months. How can they do it if they supposedly get penalized? What does penalized mean? Does it mean that they get to pay a penalty fee, or does it affect credit as well?