Errrr... I'm a little confused by what you're asking. Were you thinking the Injustice Gang would have the entire episode by themselves, with no JL? That would make an interesting series... the Injustice Gang vs. the invaders from beyond! The Injustice Gang runs for Congress! The Injustice Gang get into an irreverent argument over who ate all the peanut butter in their shared apartment!
Ahem. Anyway, just because the ep is said to focus on Batman doesn't mean that everyone else won't get plenty of airtime. And we don't know how many other JLers will be in there, but since this is a villian group, I'd say chances are good we'll see the entire league.
You read it... you can't un-read it!