If the volturi attacking Is Alice's vision how could she see?

I don't know how she can suddenly see the wolves or Renesmee - it's quite a major plot hole (though admittedly it is my favourite scene in the whole movie series).

Because she can see the volturi's desion because they are vampires and the warewolves aren't a part of the decion.

It becomes True duhhhhhhhhh

There must be enough vampires present for her to see the event despite the holes in her vision caused by Nessie and the wolves. And the important decisions were taken by vampires: first Irina then the Volturi.