EE do 4G routers.
Typically you mount their external antenna to a router they supply for the 4G data link, the router acts as a WiFi hotspot.
The performance is usually better than a mobile phone would get, or even the mobile hotspot devices you can buy that do the same. I believe they basically lift software restrictions that apply to phones and have vague memory of using multiple channels, but mostly mounting a decent antenna high up and outside does the magic. But the speed depends on coverage.
That said depending on their needs it might be cheaper to just use a mobile phone in hotspot mode, as you can get a lot of data, unlimited calls and texts, from one subscription or PAYG plan, and that benefit moves with your phone. With one fewer expenses each month, and if coverage is good the landline can go too unless it is needed for emergency support kit. Also cheap and easy to test, worst case WiFi card for the PC, I found good USB one for £11. I believe EE let you share data across multiple SIMs but always wary of relying on mobile phone company product offerings like that having had them withdrawn in the past, and their 4G router options aren't cheap.
I looked into it hard for my sister, who in the end got fibre to their cabinet, but I think EE 4G router would have been better. That said I got 30 Mbps download with EE from a cheap Android mobile phone sitting on her living room sofa, so coverage was pretty much perfect. Just their landline did the classic long loop around the estate back to an exchange that wasn't that far away the way the crow flies.
