Sorry op but you are being waaaay too easy on these ADULTS! My dd is 20 left home almost 3 years ago for work and is now studying. We had a rocky patch just before she moved out but - my roof my rules!
She was earning full time so she had to pay keep, she was raised to pull her weight chores wise (I'm afraid I suspect you did practically everything for these entitled and selfish young men) and knew better than to disrespect me or our home or there were serious consequences!
Toughen up!
You're not doing yourself - or them - any favours by not doing so!
Time they GREW UP!
I'm also the daughter of an alcoholic so I get your fears but honestly at this point that's for them to figure out
Like fuck would I allow the mess you describe!
I suspect you're ignoring sometimes and screaming at others? You need to be stern commanding (head teachers voice) telling them to clear up their mess as soon as they're done eating or whatever
"I'll do it later"
"No! You will do it right now. Messes must be cleared up immediately"
Unfortunately as they're in their 20's and I suspect you've let things slide the last 2 decades (as has their father it's not all on you) So tbh it's a bit bloody late now!
I think your only hope is maybe
Change WiFi and other entertainment passwords
Sit them down for a calm but VERY assertive (look up techniques and phrases online) come to Jesus talk with them that from now on:
Pay keep - at the VERY LEAST they need to cover the costs they incur, NOT just food but also toiletries, cleaning products, heating, hot water, electric, are you back to full council tax? How many bedrooms? (Cos if it were just you you'd only need 1 bed!) ALL of it
Messes cleaned up IMMEDIATELY
Pull their weight with chores, (you can discuss and share them out according to each other's schedules if you like but don't be manipulated into doing the bulk)
Consideration shown to ALL in the house - you and their brother - regarding behaviour and noise and disturbing when rolling in after a night out.
But...honestly I think you've left it too late and it's up to them now.
Sounds like you had bad parenting of one kind and went too far the other way, understandable I had a similar difficulty. It's hard to resist the temptation.
If cost/COVID bubbles etc are a factor they could get a place together that way they're only annoying each other!