*I AM NOT A NATIVE OR TEACHER.*
"A" is a real question. Theoretically, the one who asks such a question wants to know the answer.
"B", is not necessarily a real question. The statement has a tag question at the end, i.e. "don't you?" Tag questions, in most cases, are not real questions but they are used to indicate emphasis, politeness, a request for comment, etc.
So, when John asks Philip: "You have two sisters, don't you?", it is very probable that John knows the number of Philip's sisters and doesn't expect the answer.
The following link about this topic could be useful: http://www.englishgrammarsecrets.com...stags/menu.php
Student or Learner