Or, he could rent his home and use the rental income from it to fund a mortgage on the new home.

As long as you have have enough equity in the deal (20-25%) you could do a rate & term refinance and payoff the seller financed mortgage to get a new loan.

FHA loans will have permanent mortgage insurance unless you put down 10%, at which case the mortgage insurance can be cancelled after 11 years.

You may also see a discount fee which means you are buying down your mortgage interest rate in exchange for higher upfront cost.

Sales prices and mortgage rates make it really hard to find good deals today.Wholesaling sounds good, but you could make better money working extra shifts as a nurse.You could look for run-down properties as buy-and-holds.

I can only speculate but I suspect she either met someone she's moving in with, or decided she wants to move to a cheaper place, nicer place, or is buying a home.

I just bought a property where my lender gave a mortgage on the purchase with 20% down and a second mortgage on some stuff.

I would suggest you talk to a mortgage broker or a bank though - if those homes are zoned commercial you will probably have a hard time getting an FHA or low down Conventional mortgage.

They also have deadbolts now that you could install on every door which we have contemplated, but it's cheaper to buy lockboxes and only use them for the vacant units than buy a new lock for every single unit we manage. 

Not just because I live there but because it is generally cheaper and better neighborhoods are available.