Not sure if this will help you and sorry if this is obvious…
but if you want you could pre set up their wifi for them…
edit the wpa_supplicant.conf
When you connect to wifi the wpa_supplicant.conf file is created with your ssid’s and passwords etc etc…
So you can connect to your own wifi… then go edit the conf file and ADD their wifi …
When you first write the image to the sd card…there is no conf file because you havent connected to wifi yet (obviously)… so when done writing your sd card image… you can open the sd card (on widows or whatever) and create the wpa_supplicant.conf in the root with the info needed … otherwise just connect to wifi then edit the file.
Not sure if that helps you all that much but you can pre set it up you just need their info like SSID they would connect to and password
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
Below is what mine looks like with 2 ssid’s to choose from …
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=US
network={
ssid="SSID HERE"
psk="PASSWORDHERE"
key_mgmt=WPA-PSK
}
network={
ssid="SSID2 HERE"
psk="PASSWORDHERE"
key_mgmt=WPA-PSK
}