Needing some answers...

I am going through a difficult time and thought I might get some answers here. My husband had an affair almost nine months ago, and has now been told that he is about to be the father of this girls baby due at the end of May. The girl has decided she didn't want to keep the baby which is why she has finally contacted my husband and I with the news of the baby on the way. We have two children that are teenagers, (actually my children from a previous marriage) whom my husband is a stepfather but hasn't ever had children biologically, until now. We have cried, and talked a lot about our potential options, but what we think we would like to do will probably suprise you all. Although, not an "ideal" situation, I did tell my husband that I would raise this baby as if it were my own because I couldn't imagine his only chance of fathering a child being sent to some adoption agency or something where he would never know his real father! This is his blood child, and I can't have anymore children due to health problems several years ago. I was wondering if anyone knew anything about laws or statutes with regard to this? Is it just a matter of the mother turning the baby over to us and signing over her rights? Do we have to get an attorney? Is my husband automatically legally responsible since he is the father? Do they (the state or whoever??) make you prove paternity? Gosh, I have so many questions. I just want to make the right decisions because I love my husband very much and believe all things happen for a reason. Some just aren't the way you would have planned them right?? :) Help if you can!! Thank you very much By the way, we live in Missouri if that helps with the legal issues!