english translation: "He is sleeping ....." so wouldn't " Ele está dormindo ....." fit better here? (or does "enquanto" indicate a progress "while" something else is done and therefore the gerúndio would be redundant?)
If it's a habitual thing, like he usually sleeps every time I cook, you won't need continuous.
"Enquanto" involves two (ongoing) actions at the same time, "durante" does not.
- (1) Vou dormir enquanto (2) chove.
- Durante a segunda guerra mundial, ...