By definition, a Lease/Option is solely between the SELLER and the BUYER (YOU)
You are trying to do this because you are having trouble getting conventional financing; an the Seller knows it!
You are distressed, or you wouldn't be doing it.
The Seller may be doing it for one of two reasons; Either he hasn't been able to sell his house normally, or, he wants to take advantage of someone like you.
There is no "boiler plate" Lease/Option agreement; it will be whatever you two agree upon.
Sounds like this could be rife with RED FLAGS, nuh?