Seller financing down payment?

[Tim Schroeder]

So I want to buy 2 detached rental cabins on one property that need about 30k to make them rentable. That makes it a MFR and the bank wants 25% down. I only want to put 15% down, due to the 30k rehab expenditure (25% down plus the 30k makes it less attractive). The sellers are an elderly couple who own the property free and clear. It occurred to me to get the seller to carry a small 10% second. That plus my 15% down makes 25%

My lender says this is crazy and nobody does it and it's probably against Fannie Mae regulations.

Thoughts? Alternatives?