Any idea why I cannot see ds's iPhone on bt home hub?

[User1053051066]

Just that. I can see all other devices, and restrict their internet access and I really need to be able to do ds's too, without having to change router or internet provider.
TIA

Could he be using data rather than WiFi?

Probably using data. DS1 won't use our WiFi as it's too flakey.

We don't have 3/4g here, plus he wouldn't have enough on his package.

How old is DS? The most likely solution is that he's not connected to the hub - using a different device as a tether, connected to someone else's WiFi or public WiFi, using his data, etc.

Have a look at his phone, see if it's connected to Wi-Fi and if so, which connection.

Anchor, above, has covered all bases for you as to what's happening. Any local Wi-Fi hotspots he could connect to instead? If you have low 3G/4G coverage in your area, wouldn't be surprised if there are BT public hotspots in the area.