How my spouse can adopt my son

If you son's bio dad would be willing to agree to terminate his rights, then it would be possible to request the Court to terminate his rights and grant a step-parent adoption.  The bio-dad would have to sign a Voluntary Affidavit of Relinquishment.  But you there would also be other stops in the process.  There would have to be a home study conducted to help the Court understand if a step-parent adoption is appropriate, there would have to be criminal history checks done, and the Court will usually appoint an attorney like an amicus attorney to help the Court to understand if the parental rights of bio-dad being terminated would be in the best interests of the child.   It can be a tricky process that is difficult for someone representing themselves to navigate correctly.  I highly recommend that you consult with an experienced adoption attorney.  If the process is not contested the fees may not be as high as you expect.