Lease to purchase paying off mortgage

Hello, new to this whole area of real estate. We have interested buyers who are shy of financing at this time. We thought we would try the residential option to purchase agreement with a separate lease agreement. What date do you choose to commence the option to purchase…after the lease agreement is over? Also, how do you pay off the mortgage on the property before closing with your buyer? I am in Arkansas…the property is a mobile home with acreage. The buyers are probably in the position of paying more than what it would appraise for normally, should I adjust my price in anticipation of a bank not willing to finance the remainder due, or just let the buyer take the risk. I want to be fair but I want the sale as well. Would appreciate any comments, advice or suggestions.