That's something that should be set up before leaving. You wouldn't be able to do it away from home unless you already had remote access to a computer running at home or if your router had remote access enabled.

They would have to set it up before leaving. Or have someone in the household change their router settings to enable it and share the details with them.

If you ever look at local WiFi networks in most residential areas you will see 90%+ use the default router supplied by thier isp. Also using the default SSID and password printed on the router. Most wouldn't even venture into the routers web page to change the settings. So the likelihood someone would configure this is low.

If you don't already, change your default WiFi SSID and password. It makes it easier to share with visitors, you can use the same ones when you switch routers (saves reconfiguring all devices). It also removes the possiblity of your ISP leaking the SSID and password to anyone. If it's been printed, then it isn't encrypted when stored. Many ISPs have lost lots of customers data in breaches, many of which they resit making public.