OS2 happened before. I can never remember the timeline as I think there may still be some uncertainty but it's in the region of 50 years prior to D2. There are some gnarly continuity errors, apparently, though it's hard for me to comment especially well as I've never completely finished OS2 (as with the Zeppelin escort, I have a general hatred of overblown fights at the end and couldn't be bothered). But we shall see. A lot was made of the possible retcon thing especially with Lucian but then again there's already an enormous retcon with Lucian from my perspective in that he's a guy: mine was female in DD.
Perhaps all will be revealed in Divinity 3, which will hopefully be their next venture. And hopefully again in third-person mode, or at least given the choice: I think their current engine is certainly capable of it, anyway.