As for the problem of giving others a loan as a guarantee and being cheated into a cost loan, because my relatives are relatively simple people and don't know the law, please give me some advice.
From what you said, in the legal sense, your uncle is the borrower, and he must bear the obligation of repayment. Otherwise, you will be liable for breach of contract. As for the legal relationship between your uncle and the young man, it is caused by the loan and has nothing to do with the bank. Now only when your uncle has paid back the money from the bank can you understand the bank. If your uncle has proof that the money was given by others, you can ask him for it according to law.