Especially about “when everyone else is eating”
Thank you for that essential information.
Either the simple present or the continuous could be used in this clause. The choice depends on how the speaker sees the situation. If you don't eat when the others eat would probably not be my choice, but I can't see any ambiguity. It might suggest a habit of refusing to eat in the right context some sort of phobia about being seen eating.
-"He never eats when others eat".
We all understand what eating at a meal involves, assuming a common cultural background and seeing the meal as an occasion which involves eating.
People are eating as a continuous activity during a meal. We don't 'eat' in co-ordinated unison.
"If you don't eat when the others are eating ... ." is the only possibility.
However, to my mind, it's a most unlikely and unnatural way of expressing parental annoyance at the child spoiling his appetite.
It suggests that if the child doesn't/can't/ won't eat anything at the meal they will be punished.
That's what 'be in trouble' suggests. The child is already 'in trouble'!