You’re always welcome to donate your profits to any cause you would like.

My parents have always rented and I currently rent.

Think about your grandparents and the houses that generation used to live in with it not being unusual for 5+ children plus parents to live in a 3 bedroom house that would be small by todays standards but was normal then. 

Hope someone can help me with this one. while talking with my parents they informed me they were thinking of selling their triplex.

Also, whatever your theory/explanation is, would you recommend buying from relatives or parents who would offer you a house under fair market price, or is there a better strategy?

They are active in their communities, generous in their donations, and seasoned travelers.

@Chad Ullrich  It is not an obscure rule at all, but your lender is mistaken (no surprise if he thought it was an “obscure rule).A parent/relative as a non occupying co-borrower  is an exception to rule, allowing 3.5% down.

My parents had a rental for my brother and I (and roommates) while I was in college.

Like a sister, parent, friend.

Six years ago I went through a divorce and my parents helped me out by buying a house in their name but letting me have the equity.