OP, I get how exhausting it is - 3 teens/nearly teens here - DD (16) & 2 DS (14 & 12).
There's a lot of arguing, then if they aren't arguing there's hyper behaviour (the boys) that will eventually lead to a row too.
They also love each other & can be great so there's that comfort!
I’ve just grounded them.
I think this is a really bad idea. Being grounded, in the holidays (is it holidays in UK now? It is in Ireland but know dates differ) is only going to make everyone more cross & likely to react.
What do they fight about? Do they share a room?
You need to understand some flashpoints & try & mitigate those - possibly physically, by keeping them separate or alternating times for them to do something.
In terms of the screaming / shouting, I think you need to sit down, explain it's not ok & what the consequences are. For me, for older teens it was removing phone + corresponding household task. This meant a win for me as a job got done.
I think if you do this, keep the time short. Like take the phone for the morning - if you take it indefinitely they don't care & are not motivated to try.
Finally, make them apologise, each time - their behaviour is normal kids stuff but it's important they acknowledge it & say sorry.