I checked out a video review and the Tx can handle 10 different receivers.
Although it did not mention it, I presume as it is used for cars and boats,
only 1 receiver and its model can be moving at one time,
somewhat like a Protocab Tx that can control 9 locomotives but only 1 'in steam' and moving.
You should be able to bind several receivers, so that you separately switch on the loco to be controlled and let the other switched off.
That was my approach in the beginning with using 2,4Ghz RC for trains, with a modified Spektrum Transmitter at that time.
Or you assign a loco to a certain transmitter stick as Si proposed.
The two buttons are simply that what their imprint shows.
Power on/off buttons, only that - according to the manual - you have to press both at the same time.
____________________ modelling in 1:22.5 on 32mm and 16.5mm track
Actual project: 7/8" scale on 45 mm track