I recently set-up a TP-Link AC1750 using the WPS method with a BT router, which as far I could tell went like clockwork.

The extender is now plugged in in my living room with the main light blue and both the 2.4 GHz & 5.0 GHz lights on and blue i.e. should be working OK.

I'm on high speed BT internet with speeds of Download +/- 30 Mbps and Upload +/- 8 to 9 Mbps.

1. When I look for the extender with either my TV or mobile phone only the main router name shows e.g. if the main router WiFi ID is say XYZ123, then this seems to be the same for the extender.  Is this correct or have I missed something, should the extender have its own ID + if so what has it not been assigned and is visible? 
2. Using the above WiFi ID, which I assume ito be the extender, the link with my TV works good but when mobile phones are connected in the same room as the TV  the signla can be nothing, poor or intermittent.  Once again, the phone only sees the main ID + a good signal is sometimes indicated but connection is as described, especially when streaming TV.  Is this a bandwidth, naming issue or something else? 
3. Is it correct that both 2.4 and 5.0 GHz lights are on at the same time + do I need to choose just one of these with the relevant item being used e.g. phone or TV, or does it just use the best one automatically?

Thanks, Graham