I recently tried to get my mom to use the PWA of Word online, and she said it was "worse" than the desktop version but refused to elaborate as to why.
I know I sound like I'm being harsh on my parents, but it's not like they're stupid or anything. They have spent the last 30+ years using Windows and Microsoft Office, I don't blame them for relying on the tools that they have spent the last three decades learning; I use command line tools that have existed longer than I have [1]. I do understand the stubbornness even if it does drive me a little crazy.
[1] Yes I know that GCC and Emacs and tar and grep have gotten updates since they've been released, but so has Windows.
You're right, Office is where you will struggle.
I managed to get Winboat working on my NixOS laptop, so it's possible that if I set that up they could deal with it.
Seems like you have it all figured out though, I think I’ve shared enough help good luck.
on the positive side, if their main machine is old, there are no longer win10 updates.
I've had updates break Linux and cause things to not boot anymore, and those aren't fun, but generally fixing it boils down to rebooting to a previous snapshot [1], or logging in with the command line running like three commands.
I did try fixing the computer before we nuked it. I tried walking them through the Windows auto repair, which didn't do anything (but at least it took a long time), and I tried booting into safe mode, but it wouldn't get any farther than the regular boot did. Apparently there is a way to get into a Powershell live-boot (though I didn't know this at the time), so maybe I could have fixed it with that, anything is possible, but ultimately my solution was getting the to flash a live USB of Ubuntu, and I then mounted the drive and rsync'd everything to my server.
[1] Because Microsoft still doesn't have Copy on Write (despite being a proven and more than 20 year old bit of tech) and so they can't do good snapshotting.