What distance can the mic cover before loss of signal from the transmitter

I've had it a clear cover for an entire gym. In a crowded room, it can take some adjusting. If walls are in between the signal fades fast, but open space is very clear. Crank it.

Can i get both connecting to a mixer for karaoke? Do we have any problems if we want to buy 2 shure instead of 1 shure and 1 for another?

Yes, you can buy as many as want as long as your mixer have enough inputs for your Mic.

The switch wont turn off

I don't use the power switch on the box so I'm not sure. I turn my device on/off with electrical out switch control https://www.amazon.com/Etekcity-Wireless-Electrical-Household-Appliances/dp/B00DQDJJKU/ref=sr_1_3?ie=UTF8&qid=1486577206&sr=8-3&keywords=power+remote

Item dimensions L x W x H	10.5 x 47 x 38 centimetres
Power source	Battery Powered
Number of batteries	2 AA batteries required. (included)
Signal-to-noise ratio	150 dB
Number of channels	1
Frequency range	2050-2700 MHz
Global Trade Identification Number	00042406496070
Manufacturer	Shure
Product Dimensions	10.49 x 46.99 x 37.97 cm; 3.4 kg
Batteries	2 AA batteries required. (included)
Item model number	GLXD24R/B87A-Z2
Speaker Count	1
Size	Rack Mount
Battery Type	Alkaline
Item Weight	3.4 kg

Shure GLXD24R/B87A-Z2 Rechargeable Wireless System with BETA87A Vocal Microphone, Half Rack

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