It depends. It's not likely the Marines were aware of who knew what, so this would be irrelevant. Arguing that the occupants knew the IED was going to explode, and so they were legitimate targets won't get them anywhere under Geneva IV. What the Marines need to show is that they reasonably believed at the time that the occupants of the house presented a threat themselves.
It's not unusual for civilians to know what insurgents are up to, since the line between insurgent and civilian is fuzzy to start with (insurgency is, by definition, a civilian resistance). One of the warning signs that an IED is around is an absence of civilians nearby. The problem is that the civilians, whether because of conflicted loyalties or fear, are unwilling or unable to warn the American or Iraqi forces of impending attacks.
A woman survivor in the first house directed the Marines to the second house, indicating to them that that is where the terrorists had gone. One Marine remained to guard the woman, two Marines pursued into the second house.