Can a converter box be hooked up to 23 yr. old Mitsubishi TV which does not have the red , white and yellow coaxial cable jack hook ups, and another small TV Panasonic which also only has antenna jack or are these hopeless cases and just forget about them (tho my little Panasonic still works quite well)?

You have to have the coaxial jack hook-ups for sure.

The converter boxes have to have Coax output on cha3/cha4. I believe they also have to have composite video and audio as well.

The TV's with screw terminal inputs are 300 ohm and used twin lead. A small transformer converts these sets to accept a coax input.

There were all sorts of varieties made. Some sets had Coax and twin lead inputs that you selected on the TV itself.

Just buy a splitter from the hard-ware store

Ty:

What are you splitting?

If the Converter doesn't have coax out, then a modulator is the solution, about $12-$20.
It will convert red, white and yellow of Your Converter to coax output to go to coax on TV, Then select channel 3 or 4.