[HangingOn]

I can understand your feelings as we have dealt with them, too.
Yes, we waltzed into court (we do our own adoption paperwork) and went before a judge (who didn't know about the other stuff) who had finalized several of our adoption for us, and he said,"I would be honored to sign this adoption decree!" I admit it was very scary, but what else could we do? (we prayed a lot) We had the adoption agency behind us, so I think that the DHS didn't want to step on toes; the adoption agency had guardianship of him.
We went through court sessions where the county attorney accused us (in writing) that we were to blame; they later had to strike those paragraphs. We went through this, scared to death! But now that we are where we are, we can see how things have really gone our way; and I never want to do it again!
We have 7 adopted children and no biological children. The offender tortured the three littlest ones; then they were: 4, 4, and 8. The eight year old boy is mildly retarded and has C.P., the four year old girl had the most trauma, and the four year old boy was our newest adoptee.....can you imagine coming home and having your new brother abuse you? The older boy is recovering, but needs to be reminded of the consequences if he chooses to fall back into the old ways. The little boy is doing great; he wasn't involved much, and is a fast learner. Our darling daughter is healing, but still has "daymares?" She was badly abused.
You oldest son chose to act out his anger in a very dangerous way. Does he show any remorse? Does he have empathy for your daughter? Those are the signs that healing may be possible. I asked before, did he bond to the bio-mom as a tiny baby? Was he neglected emotionally? These are things to ask yourself.
You need to get off the guilt trip, and believe me I'm saying the same thing to myself. Your son and mine are both old enough to make decisions to change, but emotionally are they able to make those decisions? Mine couldn't care less; he's perfectly content to stay where he is (he doesn't know he is moving) , it's all about him.
Your daughter is in danger. Your son knows how much you (of course) love your daughter. He is getting back at you....you are the one he is trying to hurt. How much more could your son and mine hurt their mother than to hurt what is dear to that mother? My wife was shocked to learn how much our son hates her. He was in several placements before our home; he was neglected, and sexually abused at a very young age (baby). He never attached, normally, to anyone...he doesn't know how.
As for your adoption; your son should not even be considered in your decision whether to do it; but you must be sure how you feel about his possibly coming home and abusing the new one when he sees how much you love that child.
Are you adopting through the state? We were foster parents for almost 5 years, before we went internationally to adopt. We had 12 foster children and only one was not: RAD, sexually abused, or FAS....they all had issues that we, try as we did, could not get past. Now, with that said, we know of people who have adopted through the state and their family is making it fine. We thought if we went internationally we would avoid the bad stuff; we did with 6, and the other one nearly ruined our whole family.
About your "replacing one child with another;" this is where we let guilt have its way with us, so to speak. You do not have parental rights to terminate, so you are not throwing a child away; you are just parenting from afar. You have stated several times that you care about him and don't want him feel abandoned again. He did feel abandoned by his birth family, they all go through this. He sees your love and bond with your daughter; he can't understand why it wasn't there with his birth family. He came at a very hard age; he's holding a lot inside; so is our son. Even getting through may not help...but it can't hurt.
I am glad that our son is passive-agressive; if he were in our face with anger, I probably would not have taken it well; heads would have been rolling! But his going behind our backs, after being so nice to our face, and doing the the unthinkable, leaves us in shock. Maybe if he had been openly defiant with his anger, we could have stopped the abuse before it got so involved. But with children like ours, they will find a way to do what they want.
You did the right thing in getting him out of there....thank God your daughter is such a strong child and could come to you and tell you. We still weep over our children not telling us.
Yes, people care what others think...my wife is still dealing with this. You would in no way be replacing one child for another. Your son made his own choice to live away from home..... people are going to have different opinions about what happened no matter if they know the truth or not. We have gotten opinions and advice that would make you cry and then make you want to take a ball bat to them. We have to do what is right for us. No, we are not adopting again; we're older parents, and 6 is enough; but if we felt the "urge" to adopt again, I'm sure we would go through what you are feeling, too.
As far as "letting him down, and sending him away," you can parent from afar, like a lot of families in our situations are doing. He is already saying that you have "let him down" (picking on him) even though you continue to visit, and are involved in the decision making for him. He can only see life as about "him." You are doing everything you can, at this time: keeping your daughter safe, keeping the oldest son safe, and comforting the younger son. What more can you do? Nothing. Sorry this is so long.