In the UK "Civil Unions", as the legal term, with completely equivalent legal status to "marriage" seems to have been accepted generally, so far as I know.

So far as talking about it, people can of course use whatever words they prefer to use anyway, and do so. If gay couples prefer to say they are getting married, and send out "wedding invitations", as they sometimes do, that is entirely up to them. And I would assume that the same would apply in California, whatever happens in the way of "propositions".

As for the matter of church weddings, churches do what churches do. I'd imagine that trying to impose rules like that on a church in the States would be perilously close to overstepping the constitutional division between state and church.