How can i make counters already invisible to other players when placing them?
I think you need a movement trigger on the pieces that actions when they are placed on the map where you wish them to be invisible.
Put a movement key command on the map component and use this in the Set Trigger trait.
The trigger in turn will need to fire a key command that actions your invisibility trait (not something I know much about, sorry).
Also perhaps of use, there is a pair of properties that give the status of the piece: