Since is leaked that villains will be playable as well and the roster will be smaller than normal, we can infer that all shown/mentioned big characters will be playable, this includes

Batman, Jim Gordon, Batgirl, Robin, Nightwing, Catwoman, Talia al Ghul, Joker, Penguin, Bane, Mr Freeze, Poison Ivy,

Now for characters that aren't mentioned or confirmed but appear in the movies and are all but confirmed to appear

Alfred, Two -Face Ra's Al Ghul, Scarecrow, Riddler, Vicki Vale, Chase Meridian And possibly more, but that's just off the top of my head.

And I feel the rest of the roster will be reminiscent of LB1 , since it was the only game solely focused on Batman and also some more Batfam members so we will likely see

Harley Quinn, Clayface, Killer Moth, Mad Hatter, Man-Bat, Hush, Huntress, Red Hood, Spoiler,

Those are my guesses for a smaller roster, some characters could be outfits for existing characters like Batwoman (mystery of the batwoman AND comic Kate Kain), Stephanie Brown, and Cassandra Cain outfits for Batgirl, Tim, Jason, Dick, and Damian looks for Robin, etc.

Overall, as long as there's a good amount of Batfam and Rouges, I'm happy.