Do you have a WiFi network in your house? I know that you only have a cellular internet connection via phones, but you can have a local WiFi & ethernet network without an internet connection. In a situation like yours, I would have a local network and put things like my Apple TV on it.
Presumably you occasionally travel to places with an internet connection. When in the presence of an unmetered connection, I'd download things I wanted to watch. Home Sharing allow you to share stuff in your iTunes library (for instance, videos in iTunes on your Mac) with your Apple TV over your local network. The only complicating factor is all the devices have to be signed into the same Apple ID. Which implies that things like your Mac and Apple TV will occasionally need an internet connection, although not much data will be required to be sent.
Most wifi routers are intended to have their internet connection come in through the wired WAN port. A setup where the internet connection comes via a wifi hotspot (like a phone in hotspot mode) is possible, but a bit more complicated. It might require a fancy open source firmware for the router like
https://openwrt.org/ or
Tomato by Shibby. Something like the
ASUS RT-AC56U is both well supported by open source firmware and supports plugging in a 3g/4g modem to use as the internet connection.