It's called bond for deed in Louisiana where most of my property is. It's called contract for deed in all other states. There are sites online that you can download all the forms you need. Basically its a short term loan for someone who can't qualify just yet. Has monthly payments with balloon payment after x years. Gives them time to get their credit in order and secure regular mortgage later. You retain title till it is paid off.
However if current renters weren't interested in a lease purchase I'm guessing they wouldn't be interested in this which is basically same thing (just legalese differences). Sounds like they know they have a good thing going. I would advertise it and get someone else - that should motivate them to anti up or get out. Send them a registered letter reminding them they need to be out March 31st. Of course you need the rent and time to get new renters/buyers so you can offer them a month-to-month lease from this point forward.
However if current renters weren't interested in a lease purchase I'm guessing they wouldn't be interested in this which is basically same thing (just legalese differences). Sounds like they know they have a good thing going. I would advertise it and get someone else - that should motivate them to anti up or get out. Send them a registered letter reminding them they need to be out March 31st. Of course you need the rent and time to get new renters/buyers so you can offer them a month-to-month lease from this point forward.