Okay, just as a clarification, Kuja and Akio are something of a "splinter cell" of the Dark Master's. They both technically serve him, but each is pursuing a different agenda, each irritated by their repeated lacks in advancing because of their races. Both are Fauxen. As such, they will often undermine the others by witholding information, such as the current fact that Kuja and Akio both know that an attack is coming, simply as a way to compensate for that fact.
Now that there is a stronger force against the Dark Master, they are beginning to act more overtly, planning to betray their master and attempt to get others to do the same. Starting with Asthia, since they both know her power and both respect her somewhat.
So, Kuja, who has a very close relationship with her "children", is planning on freeing them, partly as revenge, and partly as a way to lure her to the light side.