they are coming from the restaurant ?
They are from the restaurant seems strange in English
To say the least!
Could it be that this sentence is talking about food, not people?
Where did you get the chips? They are from the restaurant.
is "the" really needed before "restaurant"?
You could say "a" restaurant as well, but it does indeed need an article.
Who are those people? They are from the restaurant.
That makes no sense at all. What does that even mean? I'm a school teacher and i can tell you that is 100% wrong! Not to mention very frustrating