My sons father wants to give up his rights to our son. We both agree this would be in his best insterst and we would both sign off on it. I would also take off child support is this possible when the child is 12 yrs.

Its not possible period. This is a frequently asked question and it should be answered in this Sticky Note:

https://www.askmehelpdesk.com/family-law/signing-over-rights-read-first-116098.html

If you have any further questions after reading it, please feel free to ask.

No it is not possible, he can not just sign off his rights, If you are remarried and a new husband wants to adopt, he can sign over his rights to allow the adoption.