@Wherehaveigonewrong29384 I have read your posts, and all the replies on this thread, with interest.
So much of what you describe is exactly like my youngest DS (14). When I tell you, I am currently living on my nerves, and barely holding it together I am not exaggerating.
I think you have had some very good advice (as well as idiotic posts from people who don't understand).
My DS behaves very similarly to yours, and can act in incredibly hurtful, disrespectful and nasty ways, to his family, and also in school. Outside of school, he is very sporty, very popular, with lots of friends. Like yours, he goes out for long periods, and is well behaved, with a good group of boys who I know and like.
It is impossible to describe how challenging is. He can be fine one minute; then something will dysregulate him and he can turn into an angry, aggressive person, who will say / do anything in the moment. It might sound like your average 'challenging teen' behaviour but it isn't - it is at a point where as a family we can do nothing together, e.g. an outing, birthday celebration or Christmas, that he doesn't ruin. It's now become a self-fulfilling prophecy, as we know it's going to happen, and say so, and he clearly hears that message that he is the problem etc and lives up to it - but honestly, I have had to say no to two family Christmas invites as I know he will end up being incredibly rude and hurtful to me or his siblings, and by extension embarrass me / affect the wider family (who I have a difficult relationship with anyway).
He can still be bright, funny, chatty and a good conversationalist but it is much less frequent. I honestly dread hearing him get up, coming home to him in the evening, and every time I see the school's number flash up I have a sick feeling in my stomach.
In my case, I'm a single parent, have brought them up myself since he was a baby. So he wasn't around his dad - who was a horrible abusive man, and while he doesn't actively engage in any parenting, does everything he can to manipulate them when he does see them. I worry endlessly that he is genetically pre-disposed to be like his father.
Other posters mentioned anxiety - that's absolutely an issue for my DS. He is extremely sensitive, and thinks very deeply about things - but no matter what you try, won't open up except very rarely - and when he does, has quite extraordinary insight. He hates being given out to or when I shout - I don't start with shouting but he pushes and pushes until it's nearly impossible not to, and then he reacts very badly.
I am in Ireland, so finally have an appointment with a private psychologist who was recommended to me specifically for situations like this. He is adamant he doesn't want to go, but even though I know I can't force him, he just has to try and I am praying he will engage.
I don't have advice for you OP, except to say that you have got good suggestions here, and from parents who get it; and also to say, that I understand all that you say, and the feelings you have. It's so so hard. I put a mask on each day coming to work and often think - if they only knew what I'd been through in the few hours before I got here. It reminds me of covering up my H's abuse before I managed to get him to leave, which makes me very sad.
I would say that all those advocating 'tough love', 'remove all privileges' etc really haven't a clue. I get why it makes sense. I have gone through all the consequences too - and he does still get them e.g. I have strict limits on his phone and all devices, because he cannot regulate himself on them, and is even more horrible if he has too much time but I have found the direct consequence-for-bad-behaviour approach does not work. He feels resentful, angry, and always that it's 'unfair' and ups the ante - in the end, he can upset me and do far more harm with his behaviour, than I can with any consequences.
While I understand what you say about your DD, and that you aren't doing it intentionally - for your DS, he almost certainly feels excluded, and 'other' in the house, with you, DD and DH being a gang in your own right. It's very hard but he is working from a place of hurt.
On the gifts / privileges, I don't agree with taking them away as a consequence, but I do think re-setting your approach is key - I do not have that kind of disposable income so it's not an issue I share, but you are spending far too much on him, and, like giving a child a lot of sugary treats, it's actually making him worse. My DS also is obsessed with money, brands, getting 'stuff', and it's horrible at times the way he goes on - nothing about the value of a getting a gift, from a sense of love or occasion, just the material value, and it is so different to my core values that it really shocks and upsets me. So I do understand the situation with your DS.
I'd also say - as hard as it is now, if you are two loving parents, and a solid family, which it sounds like you are, take heart (as I will try to!) from the posters who came through the other side and have a happier relationship with their DC.