The gestation period's more like 7-10 weeks - we got 2 pregnant girls in August 2006, and they popped in September and October.
Double check that Gwen is a Gwen and not a...what, a Gavin? Otherwise you'll end up founding a dynasty. And be warned that only one of ours seemed pregnant at first...
The vet said that we should separate the girls before the babies arrived, but I don't know if this is correct, as when the time came to put them back together, the dominant one tried to murder the other one and we never got them back in the same hutch. The dominant one was very dominant before though, and they both seemed happier living separately but nearby. We couldn't leave them with a baby each because they both had boys.
Make sure you get the babies sexed by 3 weeks - boys can be sexually active as early as that, so if they're male they need to be separated from their mums and sisters, if any. They're quite independent by then. I think you're supposed to keep them until they're at least 6 weeks old, though.
The babies are gorgeous and the mums don't mind them being handled (though give them all a day or so before you do).
If you got them from a shop, go and have a moan. I turned down the offer of the shop to take our girls back and to sell the babies on our behalf, but pushed them into giving us a hutch and run because of what the vet said about separating them.
Will probably come back and bore you some more, but er, congratulations.