In my opinion, this is NOT a good partnership for you to get into.
First, good friends very rarely make for good business partners and a bad partnership can easily ruin a good friendship. Second, he fronts all the money, his wife gets a commission when you buy, he reserves the right to sale the property, you split any out of pocket costs (non-contractor cost) and you essentially split the cash flow. There are a lot of moving parts here to complicate the arrangement.
If you were going into the flipping business and he wanted to be an equity partner, then maybe a 50/50 split of profits (after sale and expenses) makes sense.
For a long term rental, why don't you just ask him to loan you a set amount of money at a set interest rate for a fixed term, then buy the rental with conventional financing and own the deal yourself? You pay him a good return for his money (which you use as the down payment); you pocket the cash flow and own the property out right, both sides win.