Atted had sent Cyril to seek out Athena because, although he was unaware that Lexington and Kelly had already colluded with the Kafka Empire, he sensed something was amiss. In this matter, Athena clearly had a deeper understanding, and she subsequently elucidated the whole situation to Cyril in clear detail.
However, Athena got one thing wrong.
That was, the collusion between Lexington and Kelly with the Kafka Empire didn't happen after the decision to subdue Rocky, but before!
In other words, before the family meeting had decided to subdue Rocky, Lexington and Kelly had already established secret contacts with the Kafka Empire, having decided to strike at the Sky Alliance together.
It was because of this prior arrangement that Lexington and Kelly were so adamant about subduing Rocky—their actions were all in preparation for a bigger plan.
Some might wonder why such a significant affair was arranged with Lexington and Kelly instead of going through Atted, the Clan Leader.