The whole premise of A Place Further than the Universe is that Shirase's mother disappeared on an Antarctic expedition a number of years ago, and that Shirase is going to Antarctica to find her. Of the rest of Shirase's family, only her grandmother seems to be mentioned. After Kimari asks her in ep. 1 if she can really go to Antarctica, she says:
That's what everyone says. My grandma, my friends, my teachers, my upperclassmen, and my neighbors …
There is also a brief appearance of Shirase's grandmother in ep. 3, towards the beginning.
Do we know anything about Shirase's family beyond her missing mother and her grandmother? For instance, do we know anything at all about Shirase's father? There are flashbacks to Gin's past interactions with Takako and Shirase in ep. 9, but other than that, there is not much to go upon.