Help getting renters to leave or buy house!

Hey guys, please advise!! I’m renting to a couple out of state and we’re having a situation. They were originally trying to buy the house a year ago but couldn’t due to their credit, etc…we told them we’d let them rent the house for a year to figure out a plan and/or get a loan. They agreed 100% and signed a contract. The contract is almost due and they still haven’t figured out anything, they keep saying they want the house but can’t buy it. They struggle to pay the rent sometimes so we doubt they’ll be able to pay the bank for whatever their mortgage payment will be. We don’t know what to do. From our end we really need the money and have been waiting for them for a whole year. Last thing they told us is that they got an appraisal to which we don’t believe they did since they always say they struggle with money and appraisals are not cheap. Maybe they did but we asked for a copy 2 weeks ago and we haven’t gotten a response. We’re torn between giving them more time that we honestly don’t have, or just go ahead and give them an ultimatum?