Assuming he has wi-fi, I would consider a used iPad (music magpie £130) locked to the photo app, so he can't access anything else.
Assuming the photos you want to share are already on an apple iCloud account, I would create a shared album that is shared with the iCloud account on the iPad.
You can then manage the shared album with the rest of the family, so they can add/remove photos and add comments, and it will automatically update his iPad without any itervention.
Whilst there is a (looping) slideshow mode in photos, it will not pick up any changes to the (shared) album, until it's stopped and restarted.
It would also have the advantage that it could be used for FaceTime calls if he's able.
Obviously the iPad would need to be charged or left plugged in, if this was an issue I would consider an iPad that supports wireless charging. (££)
If this sounds feasible, please don't hesitate to ask me for any assistance or clarification.