4. Satire is often used to mock some bad characteristics of a person or society in general, so I'd say that one of the purposes of satire is to teach readers something about society. It might teach them how to avoid making the same mistakes the society is often making.
5. The dog is playing with her. You need to use the object case of the pronoun, and she is the subject, whereas her is the object.
6. The librarian asked my sister and him if they would talk more quietly. Again, you need the object here.
