While the official announcement hasn't been made yet, both Femi Taylor (Oola in Return of the Jedi) and Tim Dry (J'Quille & Mon Calamari Officer in Return of the Jedi) have made mention that they accepted their invitations to Celebration Europe II on their Facebook pages.
When officially announced, this will bring the Episode VI guest count to seven! We'll be sure to keep you updated on all things Celebration Europe II, so keep watching the front page for all the latest news.