First, I would never try and provide tax advice to a seller, it will get you sued, especially to a 100 year old person.Regarding seller finance, since the amount is spread out over long term, they should check with their CPA on how they are or are not taxed on the gains as well as interest on the loan.

@Brandon Weis, the reason and the only reason why they cannot use the rental income on the other units for a conventional loan is because you probably live rent free and don't have a housing expense.

I would start by talking to a lender who deals with construction loans.

Quote from @Steve Tse: @Jason Taken why are you giving me a contact of a loan officer when I am looking for insurance coverage ...? 

I've always gotten a signed "authorization to release loan info" from the owner on record. 

You can get a second home loan 10% down and look for a turn key property in FL. 

@Dan Dares TMYou can use your familyMember but they will need to be a part of the deal and the bank will most likely want them to personally guarantee the loan.

Will he co-sign on loans from banks or private lenders, or will he just say, call 15 banks?

Conventional Loan How did you add value to the deal?

Patience can be your best friend and if you attempt to over leverage a property it can come back to hurt you.Some will recommend buying subject 2 where you could take over an existing mortgage that could be at a substantially lower rate - but if the lender finds out and calls the loan that could also be very bad.