Jack's
This list is excluding Alastor, b/c I'm already in contact with his author about him.
Belethia - While he would begrudgingly respect her for her leadership, Jack would also be a little irritated with her protective attitude, and even more so with her stubbornness and short temper. Most likely he'd be the most obedient with her commands, but occasionally show passive-aggressive displeasure towards her, and would probably avoid her when he's not feeling good to begin with.
Nyla - For all that she seems to be highly manipulative and devious, Jack sees her as the most likely to be easily manipulated. Her loyalty towards Perican and her love of pastries are just so straightforwardly simple. By merit of this fact, Jack would find her downright boring, and would quite possibly ignore her existence unless she specifically tried to talk to him.
Sorena - As a fellow bird-creature, Jack would most likely gravitate towards her, especially with her calm, quiet personality. He'd see her as an oasis among siblings he largely finds slightly irritating and probably a little too intrusive. He'd probably be the most comfortable with her, and is most likely the nicest to her, as well.
Oran - Despite being rather similar to Nyla in some ways, Oran is probably a little more tolerable, simply because he gives off a more laidback feel. Jack might find the older boy a little more interesting, and maybe even respect him a little for his intellectual abilities.
Cazanna - Jack would hate everything about Cazanna except for maybe her competitiveness. As he himself is rather competitive, he can respect some good competition, but little else in her personality could possibly endear her to him. He is the youngest, so he's certainly used to being bossed around a bit, he doesn't need to be bossed around more. Her protectiveness would be just as irritating as it is with his other elder siblings, and her aggressive and selfish traits would both disgust and frustrate him. No doubt, he'd stay as far away from her as possible, and when forced to interact with her, would become ten times as irritable and more likely to act out violently or fly away without bothering to finish the exchange properly.