Original: The Borkum and Helgoland camps were "volunteer" (Hilfswillige) labor camps and the labourers in those camps were treated harshly but marginally better than the inmates at the Sylt and Norderney camps.
Simplified: The Borkum and Helgoland camps were "volunteer" (Hilfswillige) labor camps and the labourers in those camps were treated harshly but a little bit better than the inmates at the Sylt and Norderney camps.