Here is some help with quominus.
I will start with purpose clauses, which don’t use quominus, but provide a useful analogy to understanding quominus.
A normal purpose clause uses ‘ut’ with a subjunctive verb.
Caesar pontem fecit ut flumen transiret.
Caesar made a bridge to cross the river.
Sometimes a purpose clause uses a relative pronoun instead of ‘ut’, particualry following verbs of motion, choosing, sending etc.
Caesar legatos misit qui pacem peterent.
Caesar sent envoys to seek peace.
Now, sometimes a purpose clause uses ‘quo’ instead of ‘ut’, usually when there is a comparative adverb in the purpose clause.
Caesar pontem fecit quo facilius flumen transiret.
Caesar made a bridge to cross the river more easily.
What is actually going on here? Well, ‘quo’ is actually a neuter relative pronoun in the ablative case.
Caesar made a bridge, by means of which (bridge making) he might cross the river more easily.
Now, on to quominus.
Quo minus is actually two words, as so often happens in Latin with words that often are paired together.
quo is a neuter relative pronoun in the ablative case. minus is well… minus, an adverb meaning less.
quominus is used after verbs of preventing.
Caesar prohibuit Sequanos quominus oppidum oppugnarent.
Caesar prevented the Sequani from attacking the town.
What is going on here? Here is a literal translation.
Caesar prevented the Sequani, by means of which (prevention) they were less (not) able to attack the city.
I hope this helps. I find with my students that they are able to grasp new ideas like quominus much more readily when they can actually see how it works and what is going on.