Option #1 - Use the WPS button:
Many laptops & routers allow you to connect even without the password by pressing the wps button on the router right before trying to connect. Alternatively, after selecting the router on your device, when they ask you for the password press the wps button.
Option #2: Try the default password
The default password can often be found on the router itself.
Or Google router model with the words 'default password'.
Option #3 Find the password from a device that is already linked:
If your relative has other devices already connected to the router, you may be able to find the password using thier device. For example, on windows device connected to the router:
Control panel -> Network and internet settings -> Network and Sharing Center -> select router name to bring up wifi status window -> wireless properties -> security tab -> chk the box that says 'Show characters' and viola - there it is.
You may also be able to find the password by Opening the router's configuration page through a web browser on a device that's already connected via wifi, or by connecting a device with an ethernet cable.
Option # 4 - reset the password:
Note: this will disconnect previously connected devices that will have to be reconnected using the new password.