I'm sure you "know" this intellectually, but I also know how hard it is to fight the instinct/wish...
Please keep in mind that you cannot ever "fix" what happened up until this point. You can give him a new foundation to move forward, in time you will help him process, you will build new memories and experiences together...but you're not going to change the past, and you're not going to be able to fix what happened to him. It really sucks. It's easy to feel guilty or frustrated because you are trying so hard to do corrective things that "aren't working", but in many ways that's going to be like beating your head against a brick wall. Useless and painful and damaging to *you*.
Right now you are laying a new foundation over uneven ground (his past). Probably there are going to be ripple effects for a long while, and maybe forever. Try to look at this time as not so much making up for or correcting the past but establishing a new, stable connection with him. You are doing this, your hubby is doing this, you as a couple is doing is, your kids collective and individually are too, as well as the whole family unit. That's a lot of pieces, and development is going to be uneven. If you're looking at his behavior now to indicate how effective your efforts are, you're probably going to be disappointed; it's going to take him a while to truly respond, but that isn't because of you! I think the best think you can do is be stable, be loving, do the best you can, call in help, expect that things will be difficult for awhile.
Tiffani mentioned how to get a copy of the BC (as long as your DH is listed on there--I'm really sorry but I don't remember if he is or not, I think you mentioned something about that in another thread). In some areas you can even request a copy of a BC online and pay for it online. Look up the vital records department in the state your DSS was born. You might be able to fax them a copy of the custody/paternity stuff too, if your DH is not on the certificate and they need proof. Same thing with the SS dept (though dealing with social security can be a full time job in and of itself). I think it might be worth it to start investigating how to do that on your own, so you're not waiting on a social worker--it just adds yet another layer of bureaucracy (and I'm sure you're feeling up to your eyeballs in it right now) and waiting on yet another person. To get the certified copies will take some time--I lost the BCs for my boys awhile ago, and it was easy to fill out the forms online and pay online but it took about 3 weeks to get the official copy in the mail.