Thank you all for your help!
If it helps, you could go grab the Quasit scroll in the Blighted Village alchemist's basement for an extra helping hand. It's in one of the coffins.
In the last fight, I had used the scroll to summon Shovel, and he is really useful for targeting the clones (I think his design is surprisingly cute for a little demon).
2) You sneak with one character til to the point where Mayrina is caughted. Then you go to the door to Ethel's room. There is a teleporter which brings you back to the swamp. In this way you can move the whole group to Ethel with being in contact with enchanted people.
I did this in a previous game, this really saves you a lot of trouble before the fight with Auntie Ethel starts (And sneaking through her lair, you can also discover a portal to the underdark).
But once she summons the masked people, my problems start...
For 1), I seldom do enough damage within time to eliminate her. I've fought her what, four/five times? Achieved it only once. Think you need Astarion and Lae'zel outfitted and buffed (wyvern poison?).
It's the same with me, but the wyvern poison is a good idea!
I try not to shove her to her death, though. I still need to talk to her
