The red color on the LED means the batteries are running low and it is time to change them.
The CST remote control is NOT active when it is within 3.3 feet ( 1 meter) of the unit or farthest than 33 feet (10 meters).
Yes, but the maximum range is 33 feet. The configuation of your homes lay out and walls could affect the range.
No. However, both remotes will be stored in the memory of the unit, but only the one paired last will be active. If that remote is no longer functioning, the unit will consider the remote that is next in the memory bank.