Well I got brave and took a pic of the mouse litter. I can see milkbands quite visible on some. It's hard to tell if this is the result of both females are not. The one is obviously thinner, the other is a bit chubbier so I'm not sure if she's delivered or not but I suspect so. They were both on the babies when I checked but you could tell one was doing the actual nursing. Seems to be about 12 or 14 of them but I counted quick and got out of there as the one female mouse started to grab pinks and move them from the nest (obviously nervous of this big human clicking away).
http://i41.photobucket.com/albums/e2...itterMar07.jpg