Stuck in the middle somewhere

I have a commercial deal that has the potential to be a gold mine. My buddy is a Realtor, and his grandmother owns the property. She’s distressed due to the death of her husband who left her with a three million dollar mortgage when he died. The property has been listed unsuccessfully for a year now through an agent (not my buddy) and still has the listing for another two months. I have two interested buyers that I am confident I will close with one of them. My buddy’s thinking like a Realtor and just worried about commissions, the listing agent is not performing and in the way, and I have the key to the door. Now we have a verbal agreement and are sitting down on Friday to put it on paper and assign what the deal will look like. I have no idea how to approach this. Because it’s a life long family friend I want to help out his grandmother, but I need to make money as well. I don’t know how to structure this contract because I don’t want to assign a contract to the end buyer, it’s tough to get a 4.5 million dollar transactional funder, but I need something to protect my interests in this deal. I have thrown around the idea of a flex option contract to allow me to set a price then exceed it, but I’m offering some seller financing through the owner who will carry back a note on the equity she has in it. Any ideas would be great. It’s also my first time dealing with close friends so it is making this even harder because I don’t want to seem greedy or like I’m taking advantage of the situation which couldn’t be further from the truth. I appreciate the advice in advance.