The first thing you do is make it clear to hom and his father that you will not drove him to school.  When you say it, mean it and stick to it.

Let him and his father know that he will ve REQUIRED to do certain chores, if he refuses, you will remove his computer and whatever else he cherishes ftom his room.

When they push back(and they will) give both of them hell.  The kid for his lack of respect and you husband for his lack of action.

Say what you mean.  Mean what you say.  Do what you say you will do.

The kid is acting like an ass towards you because you have taught him that you will not do anything.  Your husband is checking the brat because you taught your husband the same lesson.   

And only have to do what you want. Driving him is not included. Maybe he should pay you for your services.  Play their game better than them.

Huh? He expects you to drive him to school? You are aware that NO is a complete sentence, right?  This kid is an entitled jerk because both of you are enabling him.

The most important thing - what is dad's position in all this?

I personally would disengage.  Next time he pulled the "I'm 18 and can do what I want" bullshit, I'd tell him that I'm also over 18 and don't have to do anything I don't want, and that includes driving him anywhere, cleaning up after him, buying him anything, etc.

But really, his father should be dealing with this.  

You need to talk to dad in private. Do you work outside the home?  if not, i would get a job, and tell the driving service is OK

My favorite phase. I have been raising my brother since I was 18/ him 10, he is 21 now. He tried to pull this crap with me. I billed his ass for EVERYTHING!!! Laundry, food, mileage to drive, etc. You want to act grown then become grown and realize the world owes you not a damn thing and nothing in life is free. Needless to say this changed real quick when he could not get to wrestling practice, or ROTC drills. He’s 21 and currently in Japan with the Marines tough love mama. Tough love. When he can’t pay for your services then he needs to respect your rules. I mean before cooking I would ask him you for food money? If not 25¢ can get you a cup of noodles. 

I have an adult SS with disabilities who lives with us. He won't likely ever live on his own. However, he is currently working 2 jobs (each one gives him10-12 hrs per week) and he starts welding school next month. He has tried the "I'm an adult " a few times, his father and I always have the same response " You aren't an adult until you have your own home and pay your own bills. Until then, my house, my rules- the end". 

He doesnt have a choice about working- he either has a job or his phone, tv, every thing important to him is gone. Tough love works. Time to get tough!

You can refuse to chauffeur respectfully. Assertiveness and demanding respect and help with family chores is not disrepect or aggressive. No one here suggested such a thing. 18 years no part time job? Refuses to help? It is time for serious direct intervention.