Can you share units without sharing resources? Well even if you can't I will do it like this:
Shared units with the people that are in your party. Then a trigger something like this.
Red Hero Unselect
Events: A unit owned by player 1 (red) is selected
Conditions: Triggering player is not equal to player 1 (red)
Actions: Unselect triggering unit.
This should do it... riiiiiiiight?
EDIT: An ofc make 1 for each player.
Shared units with the people that are in your party. Then a trigger something like this.
Red Hero Unselect
Events: A unit owned by player 1 (red) is selected
Conditions: Triggering player is not equal to player 1 (red)
Actions: Unselect triggering unit.
This should do it... riiiiiiiight?
EDIT: An ofc make 1 for each player.