The green arrow indicates the tower belongs to you.

The two individuals in the front are the ones who are defending the towers.  In a skirmish match, you and another guild member will share a tower to earn season points. Between both individuals, the one with more damage will earn the extra season points.

Anyone crit attacks on your tower can only be blocked by the two individuals who own the tower with their shields. Any guild members doing more damage than the two individuals who own the tower will not impact where the rewards go to.