How to share campaign forum threads with two different groups of players

I'm starting a campaign and we're going to have two different groups. The background information, homebrew rules, etc will be shared between both groups of players. I want to keep the roll20 game sessions totally separate, and I want to limit cross-talk between the groups. Is there a way to share forum threads between two different campaigns? Only I need to be able to post. Thanks!

Not really.  You could create a 3rd Game that they are all in, and use it's forum, that's about the only way I can think of.

You could simply post the text and/or images as handouts within each game's Journal tab. That's a convenient location for when the players build/level up their character sheets. Journal entries are often grouped into Handouts, Player Characters, and Nonplayer Characters. BTW, it's nice to add a blank Players Notes handout that can be edited by all players in that game room.

I second the handouts suggestion.  If you had access to the Transmogrifier (Pro Perk), you could move them between games pretty easily, but doing it manually is not terribly onerous.