I wonder if something useful here is a service like what some NASes (Synology) provide, where you 'self-host' on your PC/NAS, but also replicate to someone you know's PC/NAS. Basically, install the app on both PCs, swap keys (or authentication details) and start synching.

Cloud backup without needing cloud and it would be bi-directional so you get off-site redundancy for your data/photos. Further leveraging the SAN capability is that you could share the photos online by providing public URL's. Maybe too difficult to manage for Grandma, but if either end can share (with only authorisation provided by the other party) it might work?