A8.3 SUBSEQUENT FIRST FIRE: A DEFENDING Infantry unit/(its MG/IFE-weapon) [errata included] already marked with a First Fire counter may Defensive First Fire again during that MPh as Area Fire by flipping its First Fire counter over to the Final Fire side. Such fire can leave Residual FP but if using a MG/IFE is treated as Sustained Fire and penalized accordingly. Only Small Arms [EXC: MOL], MG, and IFE can be used as Subsequent First Fire. Subsequent First Fire cannot be attempted against any target at a range > that to the closest armed, Known enemy unit, nor outside the firer's Normal Range. Like Defensive First Fire, Subsequent First Fire options are MF/MP dependent; i.e., if the moving unit expends only one MF and draws Defensive First Fire, that Defensive First Firer cannot immediately Subsequent First Fire at it until it expends another MF. The same unit/weapon can never fire on a moving unit in the same Location more times than the number of MF/MP expended (FRD, but a minimum of once per hex) in that Location during that MPh (see 9.2). Whenever a unit uses Subsequent First Fire, it must use all MG/IFE in its possession (up to the unit's normal operation capabilities; 7.35-.353) as Subsequent First Fire or forfeit their use for the remainder of that Player Turn (barring FPF); a squad may not split its usable inherent FP from that of its MG/IFE during Subsequent First Fire unless it opts to not use the remaining FP/SW at all. A Multiple-ROF weapon cannot be fired more than once per Subsequent First Fire attack. If a unit, or any SW/Gun it possesses, uses Subsequent First Fire (or Intensive Fire) then that unit and all its SW/Guns are marked with a Final Fire counter. [errata included]
As per the blue, the squad would also be marked Final Fire.
If the squad (or MG) final fires, the other essentially does too or forfeits the shot.
You can fire both together as first fire or (barring cowering) fire them separately for first fire, then fire them together (or don't use the MG for fear of malfunction) for subsequent fire (provided you didn't cower on one of the prior shots). Once one is marked Final Fire, the other essentially is also.
You can always Final Protective Fire provided the opponent is ADJ/same hex and using enough MP/MF and you don't break yourself.