Regarding that exercise,
The judges commanded the savages to be seized and to be killed.
Iudices barbari occupare et interficere iusserunt?
Is occupare supposed to be used?
occupare to me as the sense of seizing (taking over) land, not actually seizing someone. I think the word you want is apprehendi (to be seized) from apprehendo, -ere. Also possible is rapi (to be snatched, seized) from rapio, -ere.
Also, it’s barbaros apprehendi. Remember that iubeo takes the accusative/infinitive construction. And the infinitives are passive, not active: to be seized, not to seize. Note apprehendi in my explanation above.
Best luck,
David