Another example is Joe and Mrs. Joe. His sister doesn't have her own name, and Pip never seems close with her in the language he uses. Of course, she doesn't encourage this by beating him and forcing him to do chores, etc. There is no love lost there between them. So, she is to her brother nothing much more than "Joe's wife". Joe is more of a loving and understanding figure to him than his own sister is.
Plus, Joe is the blacksmith. I am reminded of the saying, "A regular Joe." Joe, the character, fits this. He is common, uneducated, but has a huge heart. He is loving, understanding, and is able to teach Pip about life and relationships even though Joe himself does not know how to read, write, or other academic endeavors.
To answer some of your question, look at the main character, Pip. In British English, as opposed to American English, the word pip refers to the seed of a fruit. Well, what do seeds do? They grow!The type of novel Great Expectations is classified under is called a "bildungsroman" a story where a young protagonists matures physically and emotionally. Pip's name signifies that he is a seed and grows into a plant, or a more sophisticated human being. This is one way Dickens uses character names to reflect Pip's personality.