2 android communication

I want to communicate with an old smartphone with my smartphone , one is the receiver the other is the controller do not use arduino
The intention is to activate a push button via a smartphone to make a photo visible on the other (old) smartphone as long as the push button is pressed
What needs to be programmed in the smartphone apps or are there examples on the net (which I can't find)
I think I have the push buttons on one phone and the other phone but how do they communicate with each other via bluetooth of the phones
I don't know if you can understand this, sorry for my english please help
See photo, the photos are white areas that are controlled by the other phone in order to be activated via LDR to drive forward on the left or right (one white area = left or right or 2 white areas = forward)

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This is the example most often given for phone to phone communication via BlueTooth: