Ah. The mate of Quiet Rain. Such a minor character, yet he is a very interesting one at that. Hear me out on this one.
Broken Feather is the mate of Quiet Rain.
Now, he was Misty Water's older brother, and while the other kits grew up and forgot about her, Broken Feather did not. Hence why they seemed to share tongues often. The reason I believe this is because Misty Water is gray wth blue eyes, Quiet Rain's kits all are gray with blue eyes, save Gray Wing and Fluttering Bird, which the former is gray with amber eyes, and the latter is brown with amber eyes. So, it is safe, for me, to assume that Broken Feather is brown with amber eyes.
Sharp Hail could also be the brother of Broken Feather and Misty Water, sense he appears to be the same age, and possibly be an older sibling, since he seemed to have not cared when his possible brother died. He seemed to not care when Quiet Rain's kit Fluttering Bird died, because he either pretended to or was completely unaware of the fact he had a younger brother and sister, and was in fact an uncle.
Stone Song could be the oldest kit, because he seemed the least worried about his kin. Why, the only thing he says to his own nephew, Gray Wing, is this:
"I wouldn't want to set off all on my own. You're a brave cat."
Anyway, that's what I think. Tell me what you think: agree, contradict, or even have a thoery of your own to tell me.