Kids bickering have me going crazy

I've got 3 kids, 4y/o (Lucas) , 3y/o (Mylo) and 3m/o.

My baby is an absolute angel, I never have any problems with him, his literally a unicorn baby.

But my oldest two are sending me crazy.

Lucas (4) keeps doing things to purposefully annoy Mylo, most recent example : I let them watch something on YouTube, Lucas had the remote and asked Mylo what he wanted to watch, Mylo was telling him directions ( eg. up, down, right, left), Lucas was following until Mylo said that one and Lucas laughed and said no and put on the one next to it which I'm sure none of them would enjoy as it was a workout video from a channel I follow.

Also he likes to dangle toys infront of Mylo until his interested and runs away with it.

Taking mylos seat and mocks him, repeatedly does or says annoying things, literally EVERYTHING HE DOES even gets on my nerves.

Thing is Mylo isn't the type to back down and cry or come to me, he will scream at the top of his lungs and just attack, they end up in a full physical fight.

Theyre best friends one second then worst enemies the next.

I've tried splitting them up in these situations, speaking to them in turns to calm down and think about what they've done even with Mylo, I know his always provoked in these situations but he can't just go into attack mode.

Even when Lucas isn't doing something to annoy Mylo, his always up to something suspicious.

I've spoken to their teachers at school and they're both such good students and get along with their friends well, but what's going on with them then?!

I've tried to be gentle with them but these passed couple days have been bringing out the worst in me, I don't want to always be shouting at them anymore, my tone keeps getting more aggressive too 😢

Even when they're playing nicely together, Mylos a little bossy which I try to correct too but the play never lasts long because if Lucas does something Mylo doesn't agree with, there's that ear pearcing scream again which makes Lucas throw the toy at him or whatever they're playing with and there's a fight again.

Please help, I find myself counting down the hours everyday till dad comes home at atleast have some help, I go gym while they're at school for about an hour or so to let off some steam, which helps clear my head but not for long.

Idk what to do about them, or is this just normal brother behaviour? Is this what you all mean when you say it's harder when they get older? It's probably why I've been finding my baby so easy