So I've been playing the series ever since it began, and to answer your questions:
-The games are in chronological order, more or less. LoQO II is a sequel to one of the endings from LoQO, and Origin is a sequel to events from LoQO II. That said, most of the characters outside of the Royal Family changes up from game to game, and you don't
need to play the previous ones to enjoy Origin. You'd just be missing out on some of the context if you didn't play the other 2.
-LoQO and LoQO II are done (hence their F95 pages referring to them as "Golden Edition"), but Origin is still in development.
-F95 has one thread per game, plus a few mod threads. The important ones are these:
https://f95zone.to/threads/legend-of-queen-opala-i-golden-edition-swegabe.5355/
https://f95zone.to/threads/legend-of-queen-opala-ii-golden-edition-final-swegabe.5363/
https://f95zone.to/threads/legend-of-queen-opala-origin-v3-20-beta-swegabe.471/
Hopefully this helps. Also, you might want to download a savegame editor unless you're a fan of grinding (Origin alone has a sidequest that requires you to kill 30 of every enemy, and even with high level gear some of those fights can go for 5-10 minutes
per battle).