They’ve allowed the Skywind and Skyblivion projects to continue, under the assumption you’ll need to own the previous games in order to run the mod.
I thought both of those projects were explicitly not using files and models from the original games, but were instead recreating the content.
A lot of total asset replacement mods and ports require some form of check against a legitimate copy, such that they aren’t distributing copies of a game, just a way for people to modify their own copy. It isn’t a flawless legal defense, far from it, but it’s a whole lot better than just getting hit with “you’re just outright distributing a copy of someone else’s game”
They are but I heard they have to do a check to make sure you have them in your library or something. It’s been a couple of years and I’m pulling from memory.