This is a theory I had a while ago. Never told tumblr about it, but with the latest update, it seems all the more plausible, so…
The derse kids arrive at the new session much later than the Prospit kids.
Rose is Roxy are Dave is Dirk.
There is no adult Dave and Rose in the alpha session, they’re stories to tell Jane and Jake to help those two remember they’re Jade and John (Which they’re probably not, but hey, plausible!). The two use troll tech to communicate with the prospit kids, thus the appearance of Gamzee. The three meteor trolls will probably pop up in some form in the next part.
Through whatever series of events, the new session is scratched and the Alpha kids head to the beta universe. The derse kids arrive late again.
Rose is Mom and Dave is Bro.