As with combat weapons, some models carry two or more missile weapons:
If a unit is equipped with two or more missile weapons, you must choose which it will use when it is chosen to shoot during step 1 of the Shooting phase.
The entire unit, including command, must use the same weapon. Characters can always choose separately – they are not obliged to use the same weapon as a unit they have joined.
If a unit champion has the option to be equipped differently to the rest of their unit, they can choose which weapon they will use separately.