Let me translate sentence by sentence.
Second opinions (and answers) are welcome.
Qui præ nimia tristitia, strictim complosis manibus et stridentes dentibus ingemiscebant.
They groaned because of too much grief, clapping their hands tightly and creaking their teeth.
This may or may not be idiomatic English, but I hope the message is clear.
Labebantur equi in immane præcipitium, et trames artissimus pepererat/præparabat omnibus dehiscens offendiculum.
Horses fell down an enormous cliff and the extremely narrow path created a wide obstacle for everyone.
This sounds like a problem at a mountain path.
Horses fall down and a part of the path collapses, leaving a wide gap in the path.
Offendiculum means an obstacle, and in this context I think it is more likely to be a hole than a block on the road.
Dehiscens is the present participle of dehiscere, "to open up".
Either the path opens up and produces the obstacle, or the obstacle produced by the path opens up.
I cannot tell for sure whether dehiscens modifies trames or offendiculum.
It does not really make a big difference for translation or interpretation, though.
Multi vel equis, vel clitellariis, cum rebus superpositis, illic amissis, pauperati sunt.
Many lost horses or pack-saddles and the things on them and were thus impoverished.
People's possessions fell down and were lost.
I am not sure if it means short term possessions like travel gear or long term possessions if they were traveling with all they got.
As with the previous sentences, more context would help me find the most suitable translation, but this level of accuracy might be enough.
In this context, I might translate the key phrase omnibus dehiscens offendiculum as "a gaping obstacle for everyone" or something in that direction.
Or perhaps even "a hole in the path that no one could pass", depending on how you want to use the translation.