They just tweeted the voice cast, from twitter and psu:
Batgirl is being played by America Young, who has previously done voice work for Barbie shows and Monster High films. Taking on the mantle of Nightwing is Christopher Sean who voiced Kazuda Xiono in Star Wars: Resistance. Sloane Morgan Siegel who has been in multiple TV Shows will voice Batman’s sidekick Robin.
Rounding out the Knights, Red Hood will be voiced by Stephen Oyoung who played Martin Li (Mister Negative) in Insomniac’s Spider-Man. Finally, Glidart Jackson will lend his vocal talent to Alfred. He has previously worked on a number of Star Wars games.