Equity Partnerships for down payment

[Eric Trompeter]

I have a family member who is willing to be a private lender and diversify from only being invested in stocks. I don't fully understand equity partnerships. Let's say I can get a duplex for 250k with 20% down, and he offers to put in the down payment. What would be a "normal" setup as far as percent ownership for the lender, and is that just paid out every month as a percent of any cashflow? What documents go into setting this partnership up, and would it require an attorney/CPA?  Lastly, would it be possible for him to use his SDIRA ( **he is an immediate family member)?