Other continents are unknown in-game at this point. :3 But there's a possibility they exist, and we do plan on one day expanding because we have lots of ideas for other nations that we've been throwing around! >8D As of yet, though, the focus is on Le'raana, but when another continent is eventually introduced it'll definitely be a big in-game event! 8D
Currently, the precursor nation is unknown, as much of that information was destroyed or left behind, deep within Fell. And of course it's super dangerous to look for that stuff!
The person/crew that discovered Yoreiq is also unknown! 8D But people are TOTALLY free to come up with something for that. Since Yoreiq was only discovered within the last ten years, it's EASILY possible those people are still alive. 8D So anyone who wants to do anything with that is totally free to jump on that plot bunny and run with it! Heck, there's even the possibility of playing out the discovery through flashback threads. ^^
As for how the nations formed, well, Connlaoth and Serendipity formed from the nation that became Fell. They were the same people, but ultimately split over a difference in belief systems. Connlaothians have the most in common with their ancestors in "Fell", while Serenians became more of a mixed people when they mingled with fae folk in the early years--in the first generations you would see half-fae being born and the like, but that doesn't happen anymore, and they eventually sort of melted together and became their own thing. Most Serenians have very little actual fae in them--just enough from their ancestors to give them an affinity for magic and weakness toward iron. People who are actually half-fae or a large portion fae are kinda stigmatized nowadays.
Adela came about when Serenians started branching out and mingled with the tribes living out there. Eventually, they also broke away and became their own thing. :3