Is the following sentence passive or not? How can we realize is such a sentence is passive or not?
For half an hour they were occupied with eating and drinking.
I am not a teacher.
It is often hard to tell whether you have a passive verb or a copula and adjective. Take "the window was broken". If you mean that it was a window that was no longer intact, "broken" is a predicate adjective. If you mean that one of the things your cricket ball did when you hit it was to pass through the window glass, "was broken" is a passive verb.
Your example, I think, is an adjective. Nobody was occupying them. Take the sentence "They were covered in jelly." If they were just sitting there with jelly on them, "covered" is an adjective. If someone was slapping jelly on them at the time, "were covered" is a passive verb.