Not sure how they would enforce that 3 bnet limit. Even with the same credit card and billing address, you could claim that some of the bnets are your under 18 child. As long as they are playing the bnet, you should be able to pay for it, or gift time codes if they really want to be a pain in the ass. Paying for time with gold on those accounts would make this even harder to enforce.

I've heard that 2.97% change per hour is capped by Blizzard to prevent runaway changes like I imagine would have happened yesterday if not for said limit.