I do forget that it's all just Ubuntu with different faces. Ubuntu was the first Linux OS I experimented with back in the day. I installed Xubuntu, and I added the Cinnamon desktop for a different style when the mood strikes, though I mostly use XFCE. I tried Chrome OS Flex once on my laptop with a live USB and I wasn't a fan. I wanted my parents to have something closer to what I use on my PC so if issues come up, it'll be something I'm already familiar with. I can offer them the option of Chrome OS Flex, but I think it'll be hard to explain the whole "cloud" idea to them. I had a hard time explaining a Firefox Sync account to them because they use Microsoft Edge and I want them to migrate to Firefox before I install Linux Mint.

Ubuntu is an excellent choice for new users, exactly for the reason you stated.  And I agree that Linux (whether Ubuntu or Mint) would be a good choice to migrate your folks toward.  Based on their usage, Linux would serve them quite well.  Another good choice to consider would be ChromeOS Flex: https://support.google.com/chromeosflex/answer/11552529   I'm not saying it's a better choice, just another option.  Check it out, and YOU decide.  And you can put ChromeOS Flex on LiveMedia and try it before installation, just like a Linux distro.   And lastly, you ARE using Ubuntu.  Xubuntu is just Ubuntu (core OS), but with XFCE desktop tools.  Lubuntu is Ubuntu with LXQT desktop; and Kubuntu is Ubuntu with KDE desktop.  There are other versions of Ubuntu, with Cinnamon, Mate, and/or other lesser known desktops.  But they are ALL Ubuntu, and troubleshooting is nearly identical.  The only reason it COULD be different is if you are troubleshooting an XFCE, LXQT, KDE/Plasma component.  But I'd say that 90% or more of troubleshooting will indeed translate across all versions of Ubuntu, and Ubuntu derivatives.