
Look at the show. True family relationships were dysfunctional or very short-lived.
Bray & his brother Martin? Martin became "Zoot," and we all know where that led.
Ebony & her sisters? That one ended fatally.

The others kinda ended weird. Patsy & her brother Paul (who was a deaf-mute), Paul disappeared. Mouse & her brother Charlie, Charlie disappeared. Alice & Ellie...that seemed like a typical teen-sister relationship. Alice being older, trying to boss Ellie who was determined to go her own way. In the end it was Alice who disappeared, carted away by the Technos to be seen briefly (teasingly!) in Season-5.

The closest we've come otherwise have been strong love relationships.
Chyna & Xeno.
Prince & Shikra.
Arianna & Judge.
Tom-F & Jade.
And there are potentially even stronger pairings currently developing in game.
Still, it seems like our characters (or maybe it's our players?) were eager to shed any family ties and forge off on their own adventures.

And maybe that's how it should be. Still...without mom 'n dad around, brothers and sisters are a natural relationship to follow. But in a world gone crazy, guess it's just as natural that everybody would split up according to their goals and interests rather than family lines.
-Chyna
Photo source: copyright Cloud-9 "The Tribe"