It’s very possible to get deposit back, if your in-law got a good deal – deep discounts AND huge upgrades PLUS incentives. The better deal you got, the easier you could back it out, the sales agents can sell it to the other buyers. There are always some uninformed buyers around.
A friend of mine backed out a contract last year, the sales agent got mad at the very beginning, but later she sold the same house to another buyer with $30K more (with same upgrades and incentives), then she returned the deposit in full along with a good luck card…