To activate the bosses you need to kill 5 sarcs. When you killed the sarcs, the bosses will activate and will circle around(all 3 of them) in the main room, but are still asleep. To awake them, you have to do dmg on them and they will start shooting bullets. thats basically it
As others already mentioned, you want to stick at 1 boss at a time. if you're not experienced with tombs, you do not want more than 1 boss shooting bullets
Kill order Bes - Nut - Geb
Bosses are enraged when they shout a sentence :
Bes : The end of your path is here!
Nut : This cannot be! You shall not succeed!
Geb: Argh! you shall pay for your crimes!
you do not want to sit in front of them when they are about to rage. So I usually tell others to back off when he/she's in pre-rage
Pre-rage Bes : 3 pyramids circle around him (they are usually destroyed, so you dont always see 3 of them)
Pre-rage Nut : 2 green big arrows
Pre-rage Geb : 2 blue artifacts circle around him (they are usually destroyed, so you dont always see 2 of them)
edit : here's a vid where I was doing a tomb on ninja without pet.
https://www.youtube.com/watch?v=cwlrqh-5gR8Wowww.. All I needed is here.. just quick q, when they become enrage, they remain enrage till they died? or they just stand enrage an amount of time? then normal?