Okay so I'll be putting this on AO3 as a note on whichever chapter The Gang™ gets back together during, but here's my "canon" of who did what storyline in game.
Vestige Roster:
Eilíse (Daggerfall Covenant, “Breton” but really Reachman/Altmer mix, THE Vestige)
Caraelin (Aldmeri Dominion, Altmer/Bosmer)
Kalara (Ebonheart Pact but also an Arcanist, Dunmer)
My canon:
*spoilers for main story*
Eilíse did the Main Story and is The Vestige, but met Cara and Kalara during the Coldharbour storyline. All three of them can resurrect at will/are vestiges, but only Eilíse was involved in the prophecy and The Five Companions.
Cara was recruited while in The Moonless Walk (helped rescue King Dynar) and Kalara was recruited at The Great Shackle (helped rescue Vanus Galerion).
Cadwell’s Silver and Gold didn’t happen; each of them completed their respective alliance’s storyline and basically compared notes. Similar to the cinematic trailers, except none of them really care about the Three Banners War so this all excludes IC/any PvP.
Eilíse did every DLC storyline but was occasionally aided by either Cara and/or Kalara. I’ll use their initials to note who did what:
Orsinium: E + K
Thieves Guild: E
Dark Brotherhood: technically E but that's OOC for them cause they don't fuck with cults