That sounds like a lot going on.
We have a DD with high functioning SNs. We've had lots of difficulties - but we found it was no use trying to work on more than 1 thing at a time. But doing 1 thing, slowly, and getting that changed, and then moving on to something else - has slowly worked.
Could you make a list of all the things that are "wrong" at the moment.
Look at that, and decide which is the one that is most upsetting to YOU.
Do your DSs sit to dinner with you at the table? Could you talk to them about that 1 thing, and how unhappy you are, and how much better it would be if we changed it, over dinner?
Then tell them a plan to change it
So if it was, say, cups are too full:
Ask them if they realise they are too full, and what would make it easier to not make a mess.
Perhaps buy a set of mugs which have a line inside or some kind of picture inside (eg. Born to Shop range has a picture inside relevant to the outside design) and teach them to only fill the cup to underneath that picture and not to cover any part of the picture.
Show them (possibly one at a time) exactly how to make a drink properly, how to fill it so that it's not too full, and how to clean up the spill if they do spill something.
And make a rule that all cups live in the kitchen so that there are no spills anywhere else.
Once they start trying, do your best to "catch" them doing it right, and praise them for getting it right and leaving the kitchen nice and tidy.
If you can think of something positive for doing their best to get it right (not necessarily a star chart - but if there are no spills for a week, would there be something small that could reward them, and keep that going for at least 3 weeks to build the new habit?).
And then move onto the next biggest issue for the next month.
I know that is not a quick fix, but it helps them to build up their life skills, and it will have a longer term impact to making a happier household. If it can work.
Because it is not worth YOUR happiness in the long term having to look after the 2 boys without support and dealing with this as your living situation.
I know you said that they are not SN enough to need support, but would they be SN enough that visual timetables and symbols may work better for them than just talking?
Social stories to help change behaviours (so allowing thought bubbles for what people think when they see the DSs wearing dirty clothes or smell them having not had a shower), and visual timetables for new routines (like making a hot drink, only filling it to the mark, wiping up any spill with a cloth and putting that back in the sink afterwards, before going to sit and drink the drink) - we have done some visual timetables and organizing lists which we laminated and then DD could tick off each step with a whiteboard marker, which would be wiped off for the next time.
[hugs]