I think you need to talk to the neighbor and you also need to confront your DH. My mom was in a similar situation and found out that her now ex-husband had hit up everyone they knew behind her back, on the pretense that it was for her. He had no plan on paying them back. He just wanted a quick buck. She found out when she asked a friend for a small loan and friend said, "I have to cut you off. You still owe me $500 from October." Mom was mortified.
So, talk to "Uncle Val" and get the skinny on everything. Lay it all out on the table. Find out why he didn't talk to you (he may have been told you approved or you wanted DH to ask) and if he considered the loan a family loan or individual loan.
Then you have to have a serious talk with DH about why he did this, what he considers the loans to be, what YOU consider the loans (his debt) and the betrayal you feel about his actions. What is HIS plan to repay it?
At the end of it all, my mom repaid the loan to the friend because she was horrified at what he'd done and knew he would not repay it. You may end up in a similar boat. When my DH divorced, he took on half the marital debts, even though they weren't all his doing. Your DH is being shifty and you need to decide what this means to you.