Every character named here has a specific role (and presumably lines) in the episode as outlined. There are other characters present who are 'optional' to appear on screen in the episodes and are not named here. The Valar etc. who were cast last season are not mentioned here even when they do reappear.
Season 2: Ep 1 - The Awakening of the Elves
Frame: Arwen, Celeborn, Celebrían (in flashback)
Main: Ingwë, Finwë, Elwë, Celeborn and Míriel
(Other Cuiviénen elves will appear in the ensemble.)
Season 2: Ep 2 - The Ambassadors
Frame: Arwen, Celeborn, Galadriel
Main: Ingwë, Finwë, Elwë, Míriel, Morwë
Also, our first appearance/lines for Radagast [Aiwendil] will be in this episode.
Season 2: Ep 3 - The Great Debate
Frame: Arwen, Celeborn, Galadriel, possibly Elladan and Elrohir?
Main: Ingwë, Finwë, Elwë, Míriel, Olwë, Círdan, Nurwen, Eöl, Lenwë, Míriel's sister? (Tatië?)
Gothmog, Sauron and Thuringwethil all appear in this episode. None of them should be 'new' characters, but these might be Thuringwethil's first lines. She was not cast yet.
Season 2: Ep 4 - The Migration
Frame: Arwen, Galadriel, Celeborn, with Celebrían, Elladan and Elrohir (in the Mirror)
Main: Lenwë, Elwë, Celeborn, Beleg, Mablung, Olwë, Círdan, Treebeard, Fimbrethil, Finwë, Míriel, Mahtan, Ingwë
Melian was cast last season.