Please help!!!!!!

To help a friend, I dipped into my retirement account to lend money to them. He used primary residene as collateral and signed/promised he/family will pay back. But he died unexpectedly. Wife/adult children agreed to pay the debt and even wrote a check to start repayment but lawyer told them to stop b/c they didn't sign the agreement.

With the house automatically going to his widow per the deed and very little in his Estate (he told me multiple times b4 death that he transfered assets out of his name/accounts to prepare a legal battle with another party), what should I do? Is it winnable to sue for breach of contract, fraud, quantum merius? Any other options? Pls help! Thanks!!.