I don't understand the dilemma - you say they both earn good money, but your SIL has hit hard times (from which I thought you meant he was in financial difficulties) and your daughter's cutting her income. I'd suggest they go to their bank if they seriously want all the expense of a move at this time when their finances are stretched - but as bednobs says, most people have to save up for things they want. Your heading says "how can I get a mortgage" - why would you want one, it's their flat?