Re: dojo frat boys
If it's only 8 to 12 people in a dojo of 150 members, I would think them to be an insignificant group. I wouldn't worry about it too much.
None of our yudansha practice exclusively with each other. They would have gotten an earful (or more) from our late Sensei, and would get one today from the other instructors. As in many other dojo, senior members (yudansha and senior mudansha) are expected to practice with newer, less experienced members.