Transactional funding on a double close when the fee gets split two ways

You lend to the entity on the A-B contract, full stop. That LLC is the buyer on leg one and the seller on leg two, so it's the only party with a position your funds are securing. The second member has no contractual claim on your borrower's proceeds unless there's a written agreement between the two of them, which is usually a JV agreement signed before the offer goes out and not a handshake in a group chat.

How the 40% moves is where deals get ugly. Cleanest is a line on the B-C settlement statement paid to the second member's entity, disclosed to everyone on both legs. Plenty of closing agents will do that. Plenty won't, and in some states paying a person for producing a buyer looks like compensation for brokerage activity depending on how the state's licensing statute reads, which is a question for a licensed attorney in that state before anyone wires anything. If the answer is that the split has to happen outside closing, I'd treat that as information about the deal rather than a paperwork inconvenience.

On your $17k: second-leg closing costs plus a point or two on $215k for a few hours plus a funder minimum will take a real bite, and I'd want to see their actual net on the last few before believing the 60/40 is on $17k rather than on $10k.

The thing that would kill your loan isn't the split. It's the C buyer's financing. If that buyer uses a lender with a seasoning or resale restriction, the B-C leg doesn't fund and your money is out with no exit that day. Get the C buyer's lender terms in writing before you commit, every time, not once for the group.

On the shared proof of funds letter, I'd decline. Your name on an offer you didn't underwrite, to a seller you've never seen, is your reputation with agents in that market, and you can't police who forwards the PDF.