Do you have anything in writing from your grandmother that indicates she intended you to get the rent from the apartment? I would not normally advise suing family, but if you have legal grounds to do so, it may be in your best interests to consider it if you don’t want to maintain a relationship with them.

Alternatively, if you have any kind of proof at all about your grandmother’s intentions, I’d ask them why they took your money. Before you do that, I’d talk to a lawyer for advice on recovering it. You might not get it until they die/sell the house (if you put a lien on it, you would be repaid when they sell the house before they got the proceeds). You should absolutely refuse to split the condo proceeds but they may adjust their will to cut you out and you’ll want to protect against that as their house is likely worth more than the condo – and your money was used to increase its value. When you have your legal explorations, I’d also ask about interest. Given your youth, putting money into compounding interest retirement savings vehicles would grow the money your grandmother wanted to leave you exponentially by the time you retire. Having that money to invest now vs decades from now could quite literally mean millions of dollars’ difference in how much you’d have by retirement. (Of course you might not leave it in such an account but you could.