Sorry Les - Wasn't trying to imply that you amor t=your DH haven't done you best for him - more that I was trying to work out where he was coming from. If I seemed critical, I apologise - I truly wasn't't getting at you - in fact you are braver than me taking on a teen, They're hard work at the best of times, and his dad left as he was entering adolescence which must have been very hard for him (and for your DH - if he is a decent man he won't have left his child lightly).
But I do agree your DSS is a victim of his mother - I suspect that she is secretly (or openly) thrilled and delighted that he is causing so much trouble for you and your family. I also agree with there posters that he needs to be called to account for his own sake or this will escalate, and every time someone pisses him off he will steal something from them, or vandalise their property or even do something to endanger them - he won't know anything except trying to exact revenge for imagined slights. (I was also genuinely wondering how she explained the credit card thefts. She's nothing if not cunning!)
Stealing from you children - especially birthday money - is particularly appalling. I think he may be feeling jealous of them and that makes him want to hurt them. Of course if his mother gave him the support (really support - not just covering for him because she wants to hit at you and your DP) and reassurance he needs, he wouldn't feel like a cuckoo in the nest.
I think I will install a camera actually. She can't deny pure proof
I bet she will. She will argue black is white if it suits her - but the police won't.
It looks like his mother is using him as a weapon in many ways - emotionally, physically and psychologically, I honestly don't know if you and DH can ever convince him that you care about him and want him to be happy because this vindictive cow is dripping poison into his ear at every opportunity, and at the same time is neglecting him (I read your post about the school parents night - that poor boy!).
It's a horrible situation for all concerned, but you can't let your children, or your relationship, suffer because of his behaviour - and nor can you let him think he can do what he wants with impunity. I am so glad that you have the support of your DH - many fathers won't accept that their children can do anything wrong and expect their wives to cope with all sorts of bad behaviour.