Why did Winston flee parents?
The betrayal of the family bond is a chief theme in 1984. Winston fears parents because he does not want to be turned into the "Thought Police" for his subversive views. "No one dares trust a wife or a child or a friend any longer," Orwell writes.
For himself, Winston wants to retain his since of individuality. He recalls "a time when there were still privacy, love, and friendship, and when the members of a family stood by one another without needing to know the reason." Unlike most citizens of Oceania, Winston feels that in order to "remain human", a person should "not loyal to a party or a country or an idea, (but be) loyal to one another."
Winston doesn't mention his father; only his younger sister and mother are discussed. I don't think flee is the best term in this case. Winston temporarily leaves his family due to the guilt he feels over stealing food from his sister. When he returns, he has been separated (dreams -a tad unclear) from his relations. The Party must destroy the familial unit in order to remain all-powerful. The Party is responsible for Winston's detachment from his bloodline.