Sons dad died no will signed over rights age 11 son now 24 dad didn't want to payback child support of $14,000. Can he get inheritance or probate it?

My son's dad recently died we were divorced he signed over all his rights to him at age 11 due to he did not want to pay back child support in the amount of $14,000 he was a convenience father. He had no will he has a step-brother and step-sister by another mother what she is also divorced from. PS4 vehicles Harley Davidson motorcycle zero turn lawn mower trailer and a large shed $50,000 life insurance where he worked at he also will get one year of his salary supposed to be split between the children or whoever he left it to. His little sister claims since Kyle dad sign over his rights as age 11 that he doesn't get nothing. She is being very ugly to him basically gave him a TV entertainment center about to fall down and two end tables that were duct taped together. Does he need to get an attorney or can he get it probated without an attorney they don't want to try to tell him anything he's hearing from people at his work that he should probate it because they know how his dad done him