You could do the same thing but with a check to make sure there is a group from your side within the area along with the condition already posted to make sure there are no enemies near.
(((count ([getposATL thisTrigger, 250, ["EAST","entity"]] call ALIVE_fnc_getNearProfiles)) == 0) and ((count ([getposATL thisTrigger, 250, ["EAST","vehicle"]] call ALIVE_fnc_getNearProfiles)) == 0) and ((count ([getposATL thisTrigger, 250, ["WEST","entity"]] call ALIVE_fnc_getNearProfiles)) > 0) and ((count ([getposATL thisTrigger, 250, ["WEST","vehicle"]] call ALIVE_fnc_getNearProfiles)) > 0));
Hopefully that works because I got lost in the parentheses and can't test right now. It checks to make sure there are no enemies nearby and that there is at least one group from side WEST in the area.