I agree it's rather strange that Kira's surviving family (if indeed she has any) don't show up or get mentioned, given that Bajor is right next door and that she's now quite a prominent, no doubt famous, citizen. But then, given her history, I imagine Kira considers fellow resistance fighters her family more than any hypothetical aunts and uncles or second cousins. I imagine she constructs her identity along the lines of her brothers and sisters in arms, and/or brothers and sisters in faith, rather than who she shares genes with. Perhaps she truly doesn't care about any extended Kira clan or whatever her other family heritage is. Looking at it that way, I suppose we do
meet Kira's family - Lupaza and Furel are to all intents and purposes her "older siblings", are they not?
The novel explanation for the brothers always sat well enough with me, and is more or less what I assumed anyway. Since Reon and Pohl are so rarely mentioned, I decided they must have died or else become less than relevant to her. And as she dedicated her adolescence and young womanhood to the freedom of Bajor, either they were part of her motive (being ultimate victims of the occupation) or relatively unimportant in relation to that goal (because they didn't share it - collaboration or indifference, who knows?)