I'm seeing the seeds of truth in this already. The puppy got very "bitey" today when he got excited. I put him on his back and gave him a sharp stare and "naaaaaaaah!" growl (much like the sound of a basketball shot-clock). He was meek for about 10 seconds and then got hyper again... but wouldn't bite me, just my mom and my two dogs! Sadly, my big bullies just let him hang on them, and won't put him in his place. I could pet him and his tail would wag as hard as it could. My mother would reach down to pet him and he was nipping over and over. I told her to reprimand him like I had, and her version could only be described as lame! He struggled and bit at her while gently put on his back. Plan B was for her to yell "ouch" and act like the bites were terribly painful (which with those little teeth, they can be). This was actually pretty effective.
The second way this came to light was walking him on lead several times today to relieve himself. I'd give a light tug on the lead, stand pat, and wait him out before I would walk another step. When Mom took him out, he was lunging, pulling, run and jerk himself when he got some slack in the lead, and biting the leash!
It's odd, while he certainly sees me as "alpha," he still follows her everywhere during the workday. I tried to test him and have both of us squat and call him, and he came to her every time! Even if I roll a ball across the floor, he runs to get it, and brings it back to her. Granted, he goes home with her every night and spends much more time with her. But it's almost odd how this dog has adopted her. I joked that she had bacon in her pocket.