Before you allow your son to meet his biological father and attempt to have a DNA test performed, I think it is very important that you consult with an attorney as such action could have a significant effect on your son's parental relationship with your husband.
The person listed on the birth certificate is presumed to be the father of the child, until that presumption is challenged in court by a parent or potential father filing a petition to establish someone else as the biological father of the child.
You cannot force your son's biological father to submit to a DNA test, absent the court ordering him to do so as part of a petition to establish paternity.
If your son's biological father is proven to be the father as a result of a DNA test, he would have the right to seek that the court establish him as the legal father of your child, and then seek custody of and parenting time with your son. He would also have the obligation of paying child support to you for the benefit of your son. An individual cannot have two legal fathers, and in the event your husband's role as the legal father of your son is challenged in court, and your son's biological father is successful in such a challenge, your husband would no longer be considered the father of your son.
please remember that my answers to your questions are based only on the information you provide on this site, and are for general purposes only. My answer to your question does not establish an attorney-client relationship. for more information, see www.johnsonmead.com
Sign up to receive a 3-part series of useful information and advice about child custody law.