Yes, i finally got through it.
As FlamingKing suggests; to do it in a reverse order helps to get through it.
1. Kill hostiles
2. Go to the last Skritt in the back.
3. Let him revive the 2. in the middle.
4. Go to the Skritt in the beginning.
5. Then also the Harpies should spawn if you go outside.
Here was it where i was stuck:
