During the quest I got to kill a mob that spawns 2 minions called "Fallen Angel Haures".
I cannot handle him, tried inquisitor stance, tried to sleep the minions, tried to run, tried might of haven; it simply doesn't work, one time I even died, lol.
Hmm, the book you get at the start of the class change quest tells you to sleep the minions and use sacred attacks (i.e. might of heaven) on the boss. So I'd guess trance on the minions and then alternating might of heaven on the boss and major heal on yourself should work. But if you say you tried that and did not succeed, I guess you have some equipment or buff trouble. Maybe try getting some good buffs before you start the fight, e.g. cov from a clannie and some songs/dances.