I always have my phone on 4G as I get better reception even when at home. My iPad is WiFi only, so if I use my phone as a hotspot then I'll be using the phone's 4G which should work but haven't tried it yet.
You should have said that in your first post. As that puts a whole different context on this.

Given your Wifi allows you to access porn on the Ipad and not here. I would say its likely an HTTPS issue. Either that or the porn sites you are going to are obscure and thus not on any filters.
You could try changing the DNS on the Ipad to 1.1.1.1 or 9.9.9.9 as it could be your ISPs DNS blocking access to here.
If that doesn't work. Try pinging and then running a traceroute on your iPad to here (there are free apps to do so) to see which hop is dropping the packets. Try doing the same on the routers config page itself. (i.e the one usually logged in by going to 192.168.1.1)
You could also check if the date and time is correct on the Ipad as if that is not correct, you wont get into here.