
Originally Posted by
Necromas
Speculation (spoilers of Ep 202-204, duh):
-Their clan was planning against Konoha, probably an usurping or something, and the third discovered their intentions.
-The clan planned to use Yamakos powers for their malicious intentions.
-Yamakos parents were "good guys" and went against the rest of the clan, so they were killed to get them out of the way and give the clan access to Yamakos powers.
-The third decided that the best way to avoid a civil war was to seal Yamakos powers, and place her in Kurenais care, trying to keep the whole incident under wraps.