These are the canonical backstories of Uzu, Nonon, Inumuta and Gamagori; it comes straight for Nakashima’s LN that was published in this month’s NewType.
I would like to see their family. And I'm sure the producers have a concept how they could look. So, hopefully some parents will really appear later but just if there is a good opportunity in the story for them.
Someone has put out some rather rough translations of the actual Newtype stories, and sadly, those implications appear entirely correct
Newtype Translation said:
When they first met, Satsuki was still an ordinary girl. She was sensitive and pleasant to talk to, and her smile never wavered. She was a properly brought up young lady. She wasn't interesting. [...] But one day, Satsuki changed. They were in the highest class in preschool, so they were five years old. She stopped smiling. She stopped (can't read in either scans). The girl who was so bubbly and cheerful before, suddenly became like a knife deeply embedded in the ground. [...] [Nonon] couldn't understand what happened, but she thought it was wonderful. But she couldn't stand liking this change, and she pretended not to notice it.