All the above are great recommendations and we have used them all with success with Tiara. We got her @6weeks 5days old which is young by most opinions...but better than where she was. Anyway, just keep at it. She is 13 weeks and the improvement is incredible. She still wants to eat my 8 year old son, but that's his fault for being..well...8 years old. Its all about consistency. Redirect the bite onto a toy. Now that Tiara is a bit older, we are being even more stern with the teeth at all on flesh. She gets it, but its just too much for her sometimes. You can see her jaws trying to NOT bite down, like she knows she shouldn't but nature takes over. She never "bites down", but you know what I mean, she does the sharp teeth puppy nibbling.
Saying "ouch", and than turning away really works. I have used time outs when she gets too nuts with my 8 year old, she gets this Kujo look and just wont stop grabbing his clothes. I put her in the bathroom alone for 30 seconds. And man o man does she come out like it was a 20 year stint. I also have been giving her a very very light tap on the snout with one finger and saying NO BITE!. She is getting better every day. He is involved with her feedings and training, so slowly she is accepting him as a superior rather than a litter mate. It is a work in progress though.
There is hope. It does get better, trust me. Use the sound advice you find on here, read a couple puppy books and soon it will happen less and less.