Small shop brokers that have access to multiple programs so that they aren't beholden to one or just a few loan programs will typically get the most competitive product for the borrower. 

I'd sure like to borrow his MLS access (if he had it) for easier research though.

If I get nervous about the 1st 2 options, I can just not record the new deed and its like I never bought the property at auction and at the point, Merry Christmas to the old owner, because I just paid his taxes.A few things to think about nonetheless.I agree with the advice you received in point #2 since you are not a borrower or mortgagor or guarantor on the mortgage, anything on the foreclosure should not go against you at the credit bureaus.I am not sure about what you are stating in point #3.

After it’s built borrow on full value and gift the parents back the land value?

Borrow against it as needed for retirement and keep it as a high end rental if they want to vacate it.  

Ive also asked if they have other previous borrowers that I could talk and was told no for their privacy.

We've also advised this method to our investor clients that borrow from us.

Borrow from others?

And buyers can’t borrow $1 more than 75-80% of the comped value of similar non-STR homes.

If you just borrow more money, you are getting deeper in debt.