Ask for a line of credit.  

They started having a guy from a company called Pathways come to these events and get people to put 40k on 4 or 5 credit cards which put them in massive debt and wrecked their credit because of this dishonesty as well as other things said in the three days.2.

I'm also considering finding a seller that would pay more than me to help my father-in-law out and perhaps get a wholesale commission that I could use on my next (ok, first) brrrr, but I'm not sure the best way to validate a fair price or know what a fair wholesale commission would be.

If the permanent financing will allow you to recover most of your initial investment and the fair market rent covers the principal, interest taxes, and insurance with cash left over, you have a BRRRR.

THe lender is a credit union and it is a conventional low rate loan.

I'm a decent and fair guy so I appreciate the entrepreneur spirit, but to take free of charge is THEFT.

I used a personal line of credit of $8k to invest.

Whether bank or credit union - either will work. 

We have about 1/3 to 1/2 of a down saved at the moment, have a 755 Credit score, and are feeling good.

Look at Homes.com or Realtor.com to get an idea what that type of property is selling for (look at the ones Pending or Under Contract)...or, look in the county's GIS system to see what similar properties sold for.Once you have an idea what a fair market value would be, let the landlord (if they're interested in selling) mention their price.