Lost In Space

The story is set in the Soviet Union (in Russia - Perm). After the WW2, it is based on a little girl (13) and her brother (15). Their parents have died during the bombings and they went to live with their grandparents.
In the story the girl finds a recording of possibly the 1st Russian cosmonaut who was sent to space but never returned as they have burned while entering earth's atmosphere.
She tells her brother about it and that's when they start to discover creepy secrets about their family and what really happened.