Our site currently support having multiple guilds on a single site, in the form of "Guild Rosters". With that method, you would only need one site, especially since they all share the same forum and calendar.

That said, it doesn't however, currently support a way to have multiple sites all tied together, though something like an RSS feed or an XML feed for event information would be an interesting feature to join.

But if you already pretty much share everything, you could quite easily manage having multiple guilds on a single site, each with their own application and whatnot.

But if you must have them on separate sites, I'm afraid the system in it's current form doesn't do that.

Though, as I said, an RSS Feed for events is a good idea, and indeed, there are some plans for implementing integration tools with external sites.