I dont know if you have ever read my sad story of adopting a child of 11 who was clearly damaged brfore he met us and was a budding psychopath. He was very much like your strpson. He hurt animals (eventually killed our dog), threatened fires (lit tiny onesin his toom in front of our two littles), peed and pooped in odd places, molested little kids...by the time we found out the worst of it, we called CPS and told them to take him now. That day. They did. And he had never tried to kill us, not that it would have shocked us if he had.
Extremely early seperation and/or trauma in a baby/toddlers life can screw with a young toddler and childs brain wiring and the child is often severely damaged way before we try to raise them.
Three big red flags of a budding psychopath are cruelty ro animals, fascination with fire and pottying in odd places. Molesting younger kids is common. Crazy lying and stealing are. A clear lack of remorse exists.
I think your stepson may be a budding psychopath (i am so sorry) and I think that probably his social workers and other mental health professionals think so too which is why they cant tell you what to do. They dont know. To date, there is no way known to stop it. All you can do is protect yourself.
I feel he is very dangerous and needs 24/7 watching and therapy without any plans to ever come home. At 14 he is doing things most adults never do. He is very sick. There is nothing you can do other than make sure he gets 24/7 residential until he is eighteen...then dont let him too close even after that, at least not close enough to live with you
If it is hard emotionally (it has to be), please seek therapy for you and husband. You never need to go it alone. We are here too, but we are not professionals.
Love and prayers. Take care of yourselves. You deserve it. You are diing the best fir him and yourselves.