Wait until the wolves are on a mission with their Volturi handlers

The wolves do not all go on missions simultaneously. (Only ten were in the group that captured Elspeth out of Denali, for instance.) While on missions, they are sometimes not all phased simultaneously.

Does Bella's shield extend through the telepathy between different alphas, or not?

Not.

Who are the alphas? Still Rachel, Rebecca and Jacob only?)

Yes.