Are the remotes interchangeable? Just the unscrew/screw attachment for both?

Yes to both.

Not all are. I think new ones are interchangeable but the older one move less fluid. My old one with a silver barrel adjuster wouldn’t work properly on a new Stealth.

You can get them to work. It’s a bit of faff though. If using a silver adjuster with a stealth you can get more fluid into it by taking out the staple that holds the button in place, removing the button, adding a few drops of fluid directly then replacing it. Mine works fine after this, but I accept bleeding it may cause problems and mean I have to do it again.