Best way to buy a Prop from a family member

[Kyle K Walker]

Hello, I am in the process of buying a family members home. I want to figure out the best way to purchase it. I will pay under market price for it. As he is only requiring I pay him approx. 4ook ( it's worth a lot more) 

He suggest to be added to the deed for 6 months and then refi? BUT will Capital gain get me in the end? 

Or should I just purchase it the conventional way. (I'm going to convert it into a 2 family and rent it out)

Please advise the BEST way to aquire it without induring a large amount of tax or penalties.

Thank you.