Having primarily partied through my experience in iCBT2, I’ve noticed that quests do not function uniformly in parties. It’s inconsistent. The majority of quests share kill counters and pick-up counters, but there are a few that do not.
For the most part, it’s not too big of an issue. Just collect more of x item. The problem becomes more annoying when the quest item in question is RNG collected - especially when the spawns of said RNG quest collection item are limited.
If any of you have been through Greene Manor and gotten the quest ‘Big Inconvenience’ in a party, then you probably know of this to some extent. The quest requires an RNG collection of a bag that spawns one at a time in the zone that is not shared between party members.
tl;dr - Quest counters aren’t consistently shared in parties, RNG collection is asinine, and blacklist ‘Big Inconvenience’.