Borrowing money from friends/family? How much do you give them in interest?

[Joe Liu]

Hi guys, I am looking at buying a couple of buy and hold rental single unit properties with all cash. With that, I want to use mostly family and friends cash. If i were to borrow 80% of it with terms of 9 months, because the idea is to buy, fix it, rent it out and refinance it (which I am being told must be under my name for 6 months) and then pulling out the money on the refinance to pay back my family/friends. What kind of a contract do you guys use? If anyone has an example one, that would be much appreciated. Also, besides the contract, how much % do you pay them or if not on %, how much can you pay them or make this enticing for them? Lastly, at which point will I start having a problem with a bank not wanting to refinance me (after 2nd one, 3rd one, etc) and what is the bank looking at to determine this? Both my wife and I work full time steady jobs.

Sorry for the loaded question!

Thanks guys!

Joe