switching the storline in "factions"

I checked wiki before I posted this, thus I could not find the answer, I have a guild who is on the arborstone (kurzick) mission and he would like to now jump on the luxon storyline, how can he do this, he would like to get to the city "breaker hollow" on the luxon side..

He needs to keep going with the storyline as hes yet to actually enter the Faction Areas + story. Once hes finished the mission Sunjiang District his primary quests will allow him to go to the Luxon and Kurzick Areas. From there he can just travel to Cavalon and continue the story on the Luxon side.

Arborstone -> quest -> Boreas Seabed -> quest -> quest -> Sunjiang District -> Cavalon/HzH

Just keep following the mission line