I would be tempted to say something like:
‘The house is X years old and we have kept on top of maintenance during our time here and carried out X works in line with relevant regs at the time, if you want the house it costs £X - the price reflects the location, size, style and condition. We are not able to complete until our chain completes on X date.’
They’ve fucked their housing situation and are trying to make it your problem.
I would be tempted to say something like:
‘The house is X years old and we have kept on top of maintenance during our time here and carried out X works in line with relevant regs at the time, if you want the house it costs £X - the price reflects the location, size, style and condition. We are not able to complete until our chain completes on X date.’
They’ve fucked their housing situation and are trying to make it your problem.