The most reasonable inference that we can make from this excerpt is that Soviet troops were fighting somewhere else at the moment of the German invasion. And, since the Greman invasion came by surprise, the did not have enough time to mobilize their army back to the frontier to combat the Germans.
Because Pony was scared that they would split them up. He didn't want to be split up because they were family, and he didn't want to go to the home and lose his family.
