Not sure if you can disable the 5ghz band on the NowTV Hub 2 router (haven't really checked to be honest).
What i would try is to re name your SSID network name on your Hub 2 router, for example adding 2.4G on the end of the 2.4ghz Freq and adding 5G to the end of the 5ghz Freq to make it easier to identify when searching on your wifi devices so you know which is which.
This is what i have done, then on your wifi devices dotted around the house you can then select the 2.4G on your home network and if you wish disregard the 5G.
You can access the router settings be typing 192.168.0.1 in the url address bar of your internet browser and use admin and nowtv to access the advanced settings.
Then go into the wireless tab in the router settings and change the SSID name on both 2.4G & 5G and click the apply button on each.
Hopefully the above will work for you.
I have just gone into my NowTV Hub 2 router settings and if you go into the 5ghz wifi tab and untick Enable Wireless Access Point i would have thought this would disable using the 5ghz band on the router.
Wireless Access Point
Enable Wireless Access Point
The Wireless Access Point of your Hub Two can be enabled or disabled to allow wireless connection of your wireless devices. The wireless icon on the front of your Hub Two will be illuminated if it’s enabled.
If Enabled, connecting devices (computers, tablets, games consoles etc.) will be able to access the Internet wirelessly.
If Disabled, connecting devices (computers, tablets, games consoles etc.) won't be able to access the Internet wirelessly.