I have a question, if Dirk and Roxy grew up in the future. And Jake and Jane in the past. How are all Dave Jade John and Rose in the present together? (Sorry if it's infront of my face XD)

The Alpha kids’ and Beta kids’ timelines are completely separate until they meet up.    Dirk and Roxy are not Bro and Mom.  Here’s a crude rendition of the their timelines to try and help.