The below is a sentence in Harry Potter Seires #1.
Mrs. Potter was Mrs. Dursley's sister, but they hadn't met for several years; in fact, Mrs. Dursley pretended she didn't have a sister, because her sister and her good-for-nothing husband were as unDursleyish as it was possible to be.
What I want to ask is what it stands for?
'it' seems like 'her sister and her good-for-nothing husband,' but
CAN 'it' stand for people or is there something I don't know?
Thanks in advence.