Unreliable IMDb aside, Wookieepedia, which is properly sourced, only lists five VAs so far. They are:

Tom Kane as Qui-Gon Jinn and Yoda
Daniel Logan as Boba Fett (presumably the young version)
Stephen Stanton as Obi-Wan Kenobi (presumably old Ben, since that’s the version he voiced in Rebels)
Billy Dee Williams as Lando Calrissian
Sam Witwer as Darth Sidious

I think it’s safe to assume Anthony Daniels, James Arnold Taylor, Matthew Wood, and Dee Bradley Baker will be there too. I suspect we’ll get a few returning actors straight from the film but they probably won’t be the majority. For example, IMDb claims Naomie Ackie is returning as Jannah, which sounds perfectly plausible. Mark Hamill is a voice actor first and foremost, so I could easily see him voicing not just Luke but a bunch of other characters too.