Uncle has been using deceased dad’s SSN for benefits in NYC

Location: NYC. Forgive me if this isn‘t the right place to seek (possibly legal) advice. I just found out my dear friend‘s Uncle (adoptive father) has been using her real father’s (Uncle’s brother)‘s identity to get greencard benefits. Her real father passed away when she was a kid but was a U.S. permanent resident. Her Uncle has been using the father’s real name and SSN to get benefits and the worst part of it all - when her dad died, the Uncle took her and her siblings in. The youngest turned 18 last year and kicked them all out of the house, my friend and her siblings had to go to the homeless shelter. We are in NYC and she just recently found a place of her own.

Idk what to do because my friend and I are just 18 and I feel horrible for her and what she’s been through. I want to report her Uncle but I want to make sure he does face the consequences. How do I even start