if the house is being leased, but is also on the market for sale odds are there was something in the lease agreement about them having to vacate if a purchase agreement is accepted, so you are at no obligation to keep them in there, and im sure the leasee knows that if an offer is accepted they have to find somewhere else.so your in the clear....and remember offer at least $10,000 less then what there asking and have the seller cover closing costs.