What are their ages? Just wondering if its first-term overtiredness.
Ds1 is always a nightmare in the run up to this half term, from the sheer exhaustion of trying so hard all day at school. He tends to come home and take it out on his younger brother in particular and when he's not teasing and/or having meltdowns he gets totally hyper, so he winds the other two up and the chaos and noise levels go through the roof. It tends to get worse in the last hour/hour and a half before bedtime and we just have to try and manage it as best we can.
Things that have helped, have been splitting them up into different rooms and giving each one something to do that they enjoy. This usually breaks the tension and kills a bit of time as well. Ds1 is a big reader, so we usually get him to sit and read in the same room as one of us, so we can keep an eye on him, then ds2 and dd can do something quietly at the kitchen table (lego, drawing or colouring). Alternatively, getting him to do his school reading with one of us keeps him totally under wraps while the other one of us gets the other two sorted.
When its time for bed, we send one in one direction and one in another, so ds1 to the toilet while ds2 has a wash, then switch over. God forbid they shoud ever end up in the bathroom at the same time, or its world war III all over again!
My boys share a bedroom, so we can't keep them totally separate, but we send ds2 up 20 mins or so before ds1 so that he can have some quiet wind-down time before ds1 goes to bed. Then they both get half an hour's reading time until lights out.
The rules are, if anyone interferes with anyone else's bedtime routine, or if there is any teasing or fighting, those involved lose ten minutes off their next computer time for each incident. Fortunately, there is nothing as important to ds1 as his computer/nintendo time, so this is a threat he will listen to - most of the time.
We identified the things they wanted to do during wind-down time really just by asking them at an opportune moment (ie when ds1 was in a good mood) what they felt would be a good thing that they could do that would help them wind-down in the evening.
It doesn't always work and to be honest the last week has been awful, but I have to remind myself that it would probably have been worse if we hadn't worked out a bit of a routine before we got to this point.
I am currently clawing my way to the half term holiday by my fingernails and hoping things will improve after a week of pyjama days and no school related stress.
Hope things improve for you soon.