The first and third ones are, for me, the most interesting. The first one is in such great condition! Love the pedals and the thread tension assemblies on the top -- like the plugs coming out of Frankenstein's neck. So cool.
I assume that the third has a hand wheel in the center of the arm for ergonomics: the right wheel is so far from the user. I'm surprised neither has a hand crank attachments (although if motorized, I can understand why not -- it's probably detachable). I'm not sure what such a machine would be used for except perhaps frame sewing such as long arm quilting. Like you, I wouldn't want to try to move it.
Thanks for the pictures -- very interesting stuff.