Two machines stuck on Installing Updates (at the same point)

[torreydale]

If you don't get the issue from the command I supplied, but you do with the GUI, then the GUI runs a different command.  I wouldn't recommend giving up on the GUI.  It's doing what it's supposed to do.  And in your case, it's letting us know something is odd.  The GUI also more than likely produces a log even when you cancel out of the process.  I just don't know where that log file is.  Perhaps someone else will chime in.

Did you try Edit, Fix Broken Packages within Install/Remove Software?

Also consider Lite Tweaks (Menu, System, Lite Tweaks).  The Autoremove Packages and Package Cache are safe options.