jIH:

{HIvchuqmoH verengan Duj}
the ferengi ships caused each other to attack each other

ghunchu'wI':

I wrote this.

That last one is the Ferengi ships cause each other to attack or the Ferengi ship
causes someone unspecified to attack each other. In neither case does the subject attack itself.

I'm afraid can't understand this; why can't the subject (which in our
example is two ships) attack itself ?

SuStel:

[muv]chuq[moH] they (plural, reflexive subject) cause each other to join.

And if the subject can't act on itself, then the above actually means
"they (plural, reflexive subject) cause each other to join a third
party (and not each other)" ?

Okay, basic grammar lesson.

When you use -chuq, it means either the subject is plural and is doing something to each other, or the "doer" of the action is plural and is doing something to each other.

If the "doer" is not the subject, it's because you're using -moH to say that the subject is causing the doers to do the action to each other. The doers, not the causer, act upon each other.

If HIvchuq verengan Duj, then the Ferengi ships attack each other. They are both subject and doer.

If HIvchuqmoH verengan Duj, then the Ferengi ships are causing something to happen. Either they are causing each other to attack (there's no implication that they're attacking each other, just that they're attacking someone), or they're causing someone unspecified or general (there's no implication that it's the Ferengi ships) to attack each other.

-- 
SuStel
http://trimboli.name