Witsend247 what do they do to keep active both mentally and physically? The more you take away, the more bored they become, and perhaps is adding to the negativity.
Could they each have one 'thing' they do, and not use it as a punishment when being naughty? Everyone has different methods of discipline, I personally believe immediately but not long standing consequences are the best options. At the moment they have given up on achieving anything 'good' long term, because what's the point? They don't get it back, they have nothing realistically to work towards.
Don't answer to rudeness. Walk away, don't feed the attention. Same with refusing dinner, put it in front of them, if they don't eat it then they don't. Don't offer anything else, eat your own, don't mention, ask, beg them to eat. Stack bedtime, make sure the youngest is asleep first, then the next two. No devices in rooms - do any of them share a room? Divide it equally, put locks on drawers if needs be but make it clear that everyone has their own box of 'things', and no one gets to touch without permission. It sounds like it's quite a busy house, so perhaps they feel they're all a bit in each other's pockets? Having their own individual 'spaces' may help, if they don't already.