I don't know how to stop the barking, but i do think having more than one dog makes it worse, with my two they start each other off all the time. Lucy is (more than!) a tad neurotic too, so she'll wake up and yap because she thinks somethings happening, then Jarvis barks to join in, so Lucy thinks theres someone at the door and so on.
It may be with your two that it started because Molly was feeling insecure and jumpy after the op, and now they're triggering each other...
Once we've moved (theres too many visitors here for it to work) i'm going to start de-sensitising them to the door by sending OH out to keep knocking on and ringing the bell at different times, without opening it or paying any attention to them so that it looses it's excitement. Whether it'll work or not is another matter!