Other members of the household don't need to be there, their computers will happily continue downloading or uploading without them there
Not sure on the early virgin hubs, but the hub 3 has a purple light on the bottom when in modern mode. The login details should be on the bottom of it, I doubt they've been charged.
Put the hub in modem mode, and turn off WiFi on the TP and connect via cable then you can speed test safe in the knowledge no one else is connected, provided you've disconnected all other network cables.