I have done this battle several times. Always challenging. But with new update none of my tactics work: leaving a couple on bridge; putting Astarion in hide; buffs galore. It always goes the same: goth get multiple attacks (2-3 each; and I typically only have 1 fighter - Laezel) down goes Laezel; more multiple attacks, down goes my PC; and then the other 2 follow. We are level 4 characters fighting level 5 does. They always seem to have advantage.
Another thing I find can make the fight way easier is haste spores.
