Yes, when I pressed on the small red button all lights went off in the house !! obviously, i still had electricity! so as you said that's for bulbs only !!
Yes, that's right! I can switch on/off from both places "if upstairs I turn on both bulbs are on and then going on the first floor and turn them off or on again !!"
I'm sorry but which one is the link wire in my case !!??