They just need to plugit in and all done. The jitsi room will be a 6 digit random number, it's not brute force safe, but we can't ask any one to enter a pin code, this should work without mouse or keyboard and it should be easy to communicate by phone. We can use a selfhosted server so privacy should be more or les ok. If a pincode could be set with a url parameter, but I couldn't find a way to do so. If someone has seen a similar project, please advise, so we can take input.
2y later...
Oma died the following day I posted this. We hadn't had a chance to say goodbye to her, even remotely.
We provided several screens to different homes so that at least some families could talk to their relatives stuck in isolation. As we didn't put any tracking software on it, we don't know how often it was used.