Cyradon Gazetteer, not Cyradon Quarterly.
There are many throughout the world with Cyrad blood of some sort. While the Cyrads were enlightened, they were hardly celibate.
The spells most likely only allow those of FULL Cyrad blood, or if they weren't, they would update those spells and wards once they learned of somebody with Cyrad blood running through their veins (it is also possible that they picked Grayson as leader of the refugees because he has some Cyrad blood in HIS veins, and thus the spell takes those not of full blood into account).
The Cyrads are manipulators. They do not needlessly kill. Nor would they kill somebody just because that person MIGHT pose a problem to their plans. They would, instead, alter those plans accordingly, to counter any disruption that said person might cause.