Take these good advices. Tell the cousin to go and buy her own property.
These are the leeches who want to parasite onto other people's property.
If the market goes up, they'll keep quiet.
If the market goes down, they'll suddenly "need cash" and then ask to withdraw their "share" of the property. And guess who will have to buy over their "share" at "fair market value"?
The hapless couple of course. Unless they want to really liquidate and realise their losses.
And of course, being her "good cousin", you will have to be "fair", right?
Most often that will mean "book value".