I don't know how the writers have handled the elves from the previous games. Presumably it will need to be addressed for the lore book.
In a fantasy setting, an explanation for different varieties of elves wouldn't need to be very elaborate, though (lots of settings have used half-elves, light/dark, etc). Divinity 2 had a species created from elves mixed with dragons, then eventually corrupted by the effects of a necromancer tainting the magic in the area.
