Can InDesign CS6 and CC run well on Mojave 10.14.5?
You can have both CC and CS6 installed at the same time. Creative Suite works well for me on Mojave, though there are some minor interface issues.
Adobe's own website states that InDesign CC works on 10.13 and later. https://helpx.adobe.com/uk/indesign/system-requirements.html
CS6 definitely won't work on Catalina, of course. However, I'm not sure why you should need two versions of InDesign. The later one is just an updated version, which can still open old .indd documents without problem.