Aggression between House Wrens inside their nest box

One parent inspects its brood and then detects another wren at the hole entrance. It leaves the box for a second and then two wrens enter and one gets close enough to a chick on the bottom right side of the box to feed it. It's not clear if food was actually given to the begging nestling. However, the second adult to re-enter the box takes on a threatening pose and the two strike at one another with their bills. One of the adults leaves. Without us marking the individuals in some way, there is no way to know if the this was a quarrel between parents or, instead, an unrelated wren from the neighborhood was up to no good.