They aren't Obsidian is. Microsoft owns both and put Obsidian back in the wheelhouse after canceling Obsidians current projects.

As far as a remaster goes that's not a full house affair for Bethesda and they will probably send that to the 76 studio to reskin. They already made a lot of assets that will easily be recycled.

Id wager what will happen with 5 is Obsidian writes it and directs the major story lines while Bethesda provides engine and art support

I hate comments like this from people who don't know what they're talking about. Preproduction is not the same as actual production. It's figuring out what the game is going to be. Deciding on location, mechanics, story concepts, and things like that. They need this so, when they're ready to start working, they have a broad outline of what technologies and resources they will need to create. It involves only a handful of people, and it's essentially entirely conceptual.

The alternative is you wait until development is done on the previous project, and then you fire a bunch of staff while you figure out what the next project is. Then you rehire again. Obviously this is stupid and wasteful, so it's best avoided.

As for the remakes and Obsidian, it is not being handled by Bethesda directly. They'll probably be checking in and offering help, but it'll be mostly hands off.