Sorry to read about these troubles your sister is having with her ex. This sort of issue is not uncommon. Just to clarify something for me, when the property sold did your mother receive her original 65K investment back from the sale, and that your sister and ex agreed to give her an additional 10K each?? (presumably as interest on the 65K investment over 15 years). Or, are you saying they only agreed to give her 10K each as a total despite her original 65K contribution when they purchased the house? If it's the latter the 65K from your mother sounds like a gift to me, rather than an investment (even though this may have been the intention). As she didn't ringfence the 65K by registering a charge or restriction on the deeds then technically this money is owned by the registered owners of the house. I would probably speak to a lawyer first before doing anything, and if you/your mother decided to pursue it then best to operate this via the lawyer so that formal papers are issued properly. But for 10K it may not be worth it. If the facts surrounding the original 65K are stronger then perhaps it may be worth fighting for half this amount. But either way all of this is v difficult without anything written down and you may end up having to put this down to experience. Speak to a lawyer/solicitor first, a few hundred pounds spent here will be a good investment into understanding your options and chances. Good luck!