They keep my entire party perma paralyzed(1+ minute paralyzes that gets refreshed before they run out) so not really sure what the hell you are supposed to do when you cant move a single character and they just kill people off.

freedom of movement should work just fine
also by that time your saves should be good enough so they won't have too high of a chance.

Do not get close. Net and poisonous clouds, knive barriers, and all kind of area damage spells.

In my case i put an army of fire elementals there and fire balls, too.

But regarding this: you do not have to kill them. Let your advisor solve the event, then go to the hill and leave it again. The crisis should be solved, too.