Ah yeah I've read about that too awhile ago. I didn't think about it with Kish being that she's born American and wasn't really raised by her father as much as her brother.
Kish is 21 so they are close enough in age that they could have been close as children. She's been gone two years, right? I'm sure Kit would be really happy to have her back around!
Hrm... Kit lives with Pasha (her brother's best friend) because she doesn't have anywhere else to go (or didn't when her brother died)- so mebbe Alexi and Cheslav had a falling out? Or they couldn't handle another rebellious teenager? Or can you think of any other reason why she wouldn't turn to family?