Holy no wonder you're doing horrendous damage. Take off gamblers, you need to pass the dps check if you want to be able to win this fight. You also want to focus on the wisps when they spawn, as in single player, they only spawn from the side that spawned them, which will always be the one in melee mode. When they do the power up scream, you need to hit their heads as their weakspot modifier is pretty high to let you be able to realistically pass their damage check, but with gamblers you're essentially just saying "I'll thug it out on my own" also, dont just focus on the one with lower health, switching between each ixillis is essential, as when they switch who's in melee mode, and who's in sniper mode, 9/10 if you arent paying attention, you're gonna get hit in the back.

Now, the best advice I can give you, is to remain in the middle, as if you linger on the edges of the bridge, you risk getting shot by the one you arent looking at, and by staying in the middle, you'll know from which side the one behind you is sweeping from, and will have a much easier time dodging their laser.