The puppies got all of the antibodies in the first two weeks, in the colostrum. They can still nurse when you give them their vaccine, but I would wait until 12 weeks. New studies by Pfizer have shown that puppies who receive one vaccine at 12 weeks are 100% immune to the disease. This article explains it really well:
Taking The Risk Out Of Puppy Shots » Dogs Naturally Magazine. Here's a copy to the study as well:
http://cp.vetlearn.com/Media/Publica...X_01_01_35.pdf
Before 6 weeks most vaccines will be useless thanks to the mom's antibodies, but this isn't because the puppies are still nursing. It's because their immune systems are still protected from the colostrum they got in the first couple of weeks.