In the long-run, take a look at something called SyncThing... This little utility is cross-platform (macOS, Windows, Linux, Android, Solaris, BSD) and is the glue which holds my office's disparate networks together. I use it with some of our clients as well. ...and I also have it on my parents' computers and devices, with it configured to send one direction to my servers for backups, including versioning. When (not if) they overwrite a file they need, I can just pull an older version.

Chrome Remote Desktop and Anydesk are two other tools I find quite helpful with them as well. Granted, that requires they be signed onto the internet, which is a whole other discussion and lessons in frustration.