NPC for Dragonsoul is right outside the instance.
NPC for all of Pandaria Raids is in the Seat of Knowledge.
NPC for all of WoD Raids is in your Garrison on the way to your Menagerie - a blind orc beside the path.
NPC for all of Legion Raids is in Legion Dalaran - used to give the weekly quests out.
You can queue solo, as a group, or as a raid of up to 25 people.