I would recommend that you use the following code for each grenade you want to have:
grenade = "grenade" camcreate [getpos x select 0, getpos x select 1, 0]
Insert the names of the variables- I suggest you use gamelogics- for x. Alternatively you could just insert real positions (like [5833.25, 2178.91, 0]) which you
This way you don't actually have the units fire grenades, you create them "out of nowhere" but that should cause the same effect.