Since these boats are going downwind, Rule 18 does apply.  The red boat must bear off and let the overlapped boats in, even though he’s on starboard and they’re on port.  For a more detailed explanation of this situation, see http://www.sailingworld.com/from-the-experts/rules/off-the-wall-incidents-at-the-offset-mark-and-the-finish-42992.html.