I would like to know if whatever conduct rules they broke are even applicable to nonuniformed combatants.
Rep West seems to have a good handle on this, although I think the severity of punishment he suggests has been completely lost on most readers.
The Marines were wrong. Give them a maximum punishment under field grade level Article 15 (non-judicial punishment), place a General Officer level letter of reprimand in their personnel file, and have them in full dress uniform stand before their Battalion, each personally apologize to God, Country, and Corps videotaped and conclude by singing the full US Marine Corps Hymn without a teleprompter.
That would be:
60 days confinement
Loss of 1 or more grades of rank
45 days of extra military duty
Loss of two months pay
A general officer letter of reprimand is itself a career killer. It's over when there is one of those on file.