1st boss Amaus
1st mechanic is exploding aura, what you need to do here is simple, go away from your teammate because the aura will explode and deal damage.
2nd mechanic is he will summon wyverns, at 8health bar and 4th health bar. You need to defeat those dragons immediately because the dragons will buff the boss with defense, attack spd and movement speed if their not defeated as soon as possible.
2nd boss kaishur
1st mechanic is this counter stance, look at this, if he does this stance, you need to stop attacking because he will counter attack with a massive AOE that can defeat some of your teammates
so keep watch for that stance because it gets trouble some in a way.
2nd mechanic is his kagebushin technique, where he summons 2 clones beside him 1 with a red wing and 1 with a white wing. and you need to defeat 1 of those guys because when the summon gets defeated its gonna create a safe zone for the whole party and to know which 1 to defeat, pay attention to the original boss at the center because he will hold up an orb which can be red or white. if he's holding a white orb then you need to defeat the 1 with the white wing. If its red then you need to defeat the red wing