"We must blow up the bridge before the enemies cross the river."
Translation:bIQtIq luchIqpa' jaghpu', QI wIjornISmoH.
Maybe not. You started by adding "ourselves" to the English sentence when it was not present in the Klingon sentence. This whole discussion has been about how to add "ourselves" to the Klingon sentence. So that leaves us in a different place than where we started. Or am I misunderstanding where you think you started?
Right! If we were watching (whether or not we had a part in it), we could say jor QI ("The bridge blew up.") In that case, the bridge is the subject (the one doing the action). But to specifically indicate that we caused it to happen, we use the -moH suffix and now we are the subject (the one doing the action): wIjormoH ("We cause it to blow up.") Though it's the bridge that is blowing up, this sentence is now about who caused it, so the bridge becomes the object (the one the action is done to) and the full sentence becomes QI wIjormoH. We are not the ones exploding - we are the ones causing the explosion of the bridge.
Please read again the Tips & Notes for the Cause unit are at https://www.duolingo.com/skill/kl/Cause/tips-and-notes
Careful. In "we must blow it up ourselves," the ourselves meaning is different from the one denoted be the -'egh suffix. The sentence major'eghnISmoH means "we must blow ourselves up" or "we cause ourselves to need to explode" but that makes less sense so without specific context it's unlikely to mean that. To translate "we blow it up ourselves" you'd use a pronoun, like wIjormoH maH or nIteb wIjormoH whichever meaning is the one you want to convey.
corrected to fix a prefix error