I hear what you are saying op; but parenting doesn't take place in a vacuum.
Our parents wouldn't put up with it but we all parent in a different way now and that has good and bad consequences.
Your son is very clever! In order to individuate and become an independent adult, he has to cut himself off from you and he does that by going against your wishes and rejecting your values.
And what important value do you state in your op that you hold dear: you are a
hard-working family! There is your answer for why he is behaving as he is!
He may not be totally aware why he is doing it either!
What would happen if you backed off a lot?
Imho, you should not be getting involved in whether or not a sixteen year old wakes up or not or whether he has a shower or not. Or whether he brushes his teeth.
If he wanted to smell horrible at his appointment that is his business.
If he chooses to get toothache then so be it. For that matter, if he doesn't make it to his appointment himself that is his choice and he gets to suffer the natural consequences eg very little money.
By facilitating all of this stuff for him he is able to shift blame on to you and shirk responsibility. Why not completely reverse tactics and back off completely?
Try not to give him so much power over your emotions. This is an awful utterly hideous phase but it will stop when this period of brain plasticity ends at around 25 years old.
At the moment he isn't capable of perceiving what a complete shit he is being, or the devastating effect it is having on you. So don't take it personally.
You and your husband go out for your birthday. And keep going out with your other dc and leave him alone in his room if that’s what he wants. Do not always tell him where or when you are going. Be a bit selfish and focus on your own life and stop the negative cycle. Let him see you and your DH enjoy yourselves. You are giving your ds too much power otherwise.
Disengage. Don't do his washing.
Tell him meal times but he can join you or not. Leave bowls of food for him in the fridge that he can heat up in the microwave. Leave out a bowl of fruit and a tin of biscuits. Bread and cheese. He won't starve. Don't clean his room. Go a bit 'cold' on him. Don't be as available. Communicate in a calm factual brief manner.
If he starts playing up then you and your DH walk out immediately. Walk out of the house if necessary and go to the pub.
Don't get drawn in to arguments ever.
Ignore, ignore, ignore.
The only time you intervene is if he engaged in risky behaviour such as drug taking then you swoop in fast and furious and the phone goes. And obviously any
physical child to parent abuse is unacceptable.
Seek advice from : www.pegsupport.co.uk/
Personally though, in general, I would give him his phone as that is his contact to friends, the outside world, his music, his alarm clock, his everything.
But other than that he is on his own.
And give him as little money as possible for him to survive without resorting to criminality. And cut the wi-fi from time to time.
Tell him you expect him to get a job or study. Give him a deadline of a few months and tell him if he needs support with it then you are happy to help.
Choose a calm moment and tell him loud and clear that you love him and want him to have a great future but you realise that his recent behaviour of being vile pushing you and your DH away has demonstrated that he no longer wants as much direction from you so you are going to let him get on with it. Then back off!
Tell him you will be interested to see what he does with his life.
You are no longer parenting from the top down but as an interested spectator walking alongside him curious to see what he will do next.
Obviously engage positively if you see him doing anything good, otherwise leave him to it. Let him know that he will not be welcome to stay at home indefinitely if he is not studying or earning.
You can't chuck him out ATM though
op. He's your child. Being there alongside them and seeing them struggle and protest and fuck up is literally what parents are there for.
Words cannot fully describe how soul-destroying and mentally draining this phase is but stick with it, albeit
at a much less engaged level.
And not at the expense of your own mental health.
He needs to see you model strength and a degree of positivity atm, the last thing he needs is for you and your dh to crumble. He is testing you in a way and you need to demonstrate tenacity.
(Obviously you don't have to put up with physical abuse though, see link to PEGS above.)
As for the autism/ADHD question, I would definitely try and get him to see a licensed psychologist specialising in this area.
And get him assessed if he will cooperate.
Of course it's a possibility.
I am surprised that so many parents of autistic children, of all people, on this thread, do not know that the effects
of autism are manifested in many different and various ways according to each individual child.