Perhaps you can let them edit their files locally and instead of vim, teach them how to scp/rsync the files onto your server. Hopefully their computers are at least fast enough to run VS-Code.
Notepad++ (for Windows, there's similar things for other platforms) at least has ability to transparently deal with remote connections, maybe that would be good option here.
My mid end computer isn't fast enough to run VS code.
mid end by which standards. my notebook is getting pretty low-end by today (i5-4200U) and it just runs fine...
A raspberry pi can run VS Code so I'm a bit curious what you call a mid end computer.