You could always use "Pick instance with UID" along with Choose(0,1,2,3,4,5,6,7,8,9,10,11,12). I tried multiple ways to use random(0,13) but random doesn't seem to work well with Pick UID...
Of course the UID numbers I use assume your spawners are the first 12 sprites made in the project, otherwise you will need to use your UIDs.
but then if your spawner objects are all the same instance you could just use "Pick random instance".
Regardless, you will need to choose the spawn point first and then fire off the spawn.