SSI is untouchable.
You attach his estate
You still owe the back support. Once the child reaches the age of majority (as defined by the support order) there will be no continuing obligation.
Place a lien on his estate
It happens. However your child support obligation may be offset by the back child support you are due unless that amount has been forgiven by the courts.
The support is still owed and SS benefits of any sort are subject to garnishment for child support obligations.
Such decisions are left to the discretion of the presiding judge.
If it isn't your check, then you can't tell if the child support was diverted to your account held by the agency that monitors such things.
The court and the mother have to agree to that you do this and you continue to pay child support incl the back support if there is any until the child is adopted. You will no longer have any rights to the child.
I doubt there were many child support laws back then. Normally, only the custodial parent of the child can file for child support, not the actual child.
yes
Yes, they can. n
Yes.