No wonder the eight great families are declining. They have become degenerates.
The greed of totalitarian dominance evolves into paranoia over the ages. Even the strongest warrior ages in time, and decay is hard to accept. The pride of being first place is like a curse, in much the same way that getting 99% is much less rewarding than getting 100% on an exam.
In this case, reason and morality lose all meaning, much like a child throwing a temper-tantrum, the prideful are most prone to petty negligence. The family see their past achievements as merits that are eternal, and feel their word is creed. Having an 18 year old display such foresight, strength and rebellion, it's their kryptonite. This is a common theme even in our modern world.