Step parent adoption

Speak to a lawyer.

Offering legal advice is against tos.

Even if it wasn't your question is very vague, different countries and states have different laws and regulations, what may be good avice in Denmark could be really bad advice in Texas.

Obviously through a lawyer! The bio dad has to give his consent, which doesn't sound like a problem. You make application for you and your husband to both adopt. At least, that's what happened in my case. But izzy's right - it depends on your country or state's laws. Consult a lawyer.