Ship them a preconfigured router and an already-set-up iPad (with the WiFi router's SSID/password preloaded) along with some printed instructions and pictures o

Ship them a preconfigured router and an already-set-up iPad (with the WiFi router's SSID/password preloaded) along with some printed instructions and pictures on how to plug the router in and how to open up FaceTime. If you want them to use only the video call functionality, you can turn on Guided Access, which can lock the iPad into one particular app, so you could pre-open FaceTime for them. Or you could ship them (along with the router) an Echo Show or a Facebook Portal (I think the Portal is easiest to set up and use). This is about as simple as you can get for video calling, but these devices aren't very portable.