First of all, this does not describe to all of the Pockets. It does not apply to Matthew and Herbert.
The rest of the family (these are Miss Havisham's relatives) are described with these words in Chapter 11. This is because they are all fakes and what we would call "suck-ups" -- people who will flatter someone when they hope to get something from that person.
All the Pockets do is hang around Miss Havisham, hoping to get her money when she dies. They will act like toadies because they hope to get something from her. They are humbugs because they are trying to fool her into thinking they care about her.