My Dad Received An Amended Child Support Claim Saying He Owed Pay Back Child Support That He Legally Paid Years Ago. He's 76.

Location: New York State. Erie county. Sorry it's long, I'm freaking out.???? My father has two daughters (Kay 48 and Val 42) from his first marriage and when he married my mom, raised me and my sister (49 and 47). They lived full time with their mom and spend weekends with us. He was behind on child support but I remember knowing that my parents had it paid off by the time I was in my early to mid 20's. Our family had a contentious relationship and I don't speak to Kay. Val went no contact with everyone for her sanity. I respect that but it hurts. My oldest sister Kay is a narcissist. She's a theif, liar and a manipulator. She stole Val's ID and ran up 10k of debt in her name. She stole from my parents, my uncle (when she worked for him) and many others. She has burned many bridges. My parent split in 2019. My mom moved and my sister Kay took my dad to a nursing home where she looked out for him. In the end she became POA and stole his veterans benefits and social security until she was caught by the staff because my dad couldn't pay his rent. He refused to press charges so they removed her as Payee and took over. When I found him, She hadn't seen him in over a year. He was depressed so I moved him to a better place. Recently as I'm trying to get finances in order he receive two notices for old child support that had my sister Val as the recipient to receive payments since their mother died over 10 years ago. Could my sister Val somehow filed a claim to amend the child support claim to get more money from my dad? She stands to get 8k but I plan on fighting it but don't know how. I also planned on filing an elder abuse charge since she stole from him. This wage garnishment will prevent him from paying the back rent he owns since we struggled to get the housing transition worked out in time. I'm scared he's gonna be tossed out from the place he loves. I can't afford to take him in. I can barely afford to take care of myself. Any advice on what I can do? Can I sue my sister? How can I find out when the case was activated and by who? How to fight it? Any advice is appreciated and sorry it's so long! ????