Loaned money to family- refusing to pay back

Our uncle ( mom’s brother) borrowed money as a debt from me and my sister ( 50K). It has been 3.5 yrs and when we ask, he says he is in financial trouble and he will pay us in his life time. We live in USA. My mom lives close to him in another country. She is going through a surgery and we want to pay for her surgery, so asked her to take the portion of money he owe us. He gave her (6K) though she asked for 10 K. When my sister sent a text to him very politely that when can we expect the rest and asked him to deposit that amount in the bank for my mom so that she gets interest for monthly expenses, his wife sent a bit nasty email that how our grand parents helped us and we shouldn’t be asking the money back, which is not true) . Very likely he will not pay us back. Not sure how to process this and not to get stressed out. My aunt called us and says, we need to suck it up as we have so much money ( some how she knows we have a lot!!..) we live in different country and they are under the impression that we are filthy rich that they can take advantage off.
How to emotionally handle this nonsense. My sister and I wrote a letter but never posted it yet. Just the thought of his behavior, whom once respected the most and never thought he will cheat us is painful. Losing money, relationship .
Guide me with some bridging thoughts to cope with this