Keep the ME Super and the MZ-5N.
ME Super because it is a classic, one of those models that brought Pentax to stardom. It features aperture priority as well as manual exposure. A good basic manual film SLR with some added features. A very nice package.
MZ-5N because this too is a classic and because I have it also.
This was the follow up to the award winning camera of the year MZ-5, with added features such as depth-of-field preview. A great camera in it's days with an excellent metering system.
With MX-50 I presume you mean the MZ-50, in the US called ZX-50. Now this was a less advanced model with pentamirror box instead of the pentaprism viewfinder in the MZ-5, and it has a limited backwards compatibility with older pure mechanical manual lenses. It lacks many of the features found in the MZ-5 and has a simpler metering system. Sure it was a fun and enjoyable entry level camera in it's days and quite popular, but the MZ-5 is simply a better camera.