Dungeon party size
Dungeons can be played alone or in a party of up to four players. Quest progress inside dungeons is shared among the party.
This gives a clear group size to plan around, without assuming that every activity in the game uses the same limit.
Can you play the story with friends?
Producer Ham described both the main story and dungeons as content that can be enjoyed solo or with a small group. That establishes the direction of story play, but it is not a promise that every campaign segment can be completed together.
Do not plan a full campaign run around the assumption that no forced-solo sections exist.
Peace and Conflict channels
The October 29 party changes include keeping a group together when members move across Peace and Conflict channels, and the ability to move to the party leader’s channel. Some sections that were previously solo are also intended to support parties.
A group remaining intact and its members being in the same channel are separate concerns. Check where the party leader is before starting an activity together.
Solo play
Solo dungeon play is supported. You do not need a four-player party simply to enter the announced dungeon content.
Read the PvP channel rules before moving a group into a Conflict channel.