Borrowing Credit, not money? Creative financing

[David Wilson]

So I have a creative financing situation that I need some help with.

My Brother in law and I are flipping houses together and our father in law is our contractor help, but also has some investing potential. 

He has some property that he owns free and clear, and we've discussed about him getting a HELOC against it, but here's the complicated situation, He makes enough money with his retirement to be able to borrow about 350k against but his credit isn't currently in good enough shape to get a HELOC. We could just do a straight up refi, but we like the HELOC idea so we only have to pay on the money we need at that time. (And I know thats a whole other discussion to be had) but what I'm asking advice on is this:

One of our family members has Excellent credit and makes way more than enough to qualify for the HELOC if we put him on the deed to the property. What we want to pitch to him is doing that so we can access the money we have in this property, but what our dilemma is, is what to offer him for compensation. we are currently structured profit splitting by thirds (Father in law, Brother in law, myself) and someone mentioned offering him 25%, but I feel like that is way way too much for just allowing us to use his credit.

So my ultimate question is--What would be a fair offer for him as compensation for risking his credit, but ultimately none of his money?

I was thinking something in line with private lending 7-12% but what dollar amount should we base that on?

What would you do in this situation?  I know ultimately this decision is ours, but I'm really interested in other ideas to brainstorm off of.

Thank you in advance!  I'll try to reply as quickly as possible!