Question: How would Nick have been able to get Libby's life insurance policies if he faked his death?
Answer: Libby's best friend, Angie who was Nick's mistress, she most likely claimed it being the child's legal guardian. Which Libby gave parental control of him.
Question: Was Angela a part of the framing of Libby? Her living with Nick seems to either indicate that she either was or at least knew about it.
Answer: Obviously, she was in on it. They were having an affair, and she moved out of state after she got the money for Matty. When Libby found out, she was in San Francisco and called Nick. She told him to be quiet and changed her last name.
Answer: Nice didn't get Libby's life insurance; he collected his own life insurance by faking his death. Libby never died, so how could he collect anything from her? I'm assuming you mean the woman he was having an affair with, named Rachel. At that point, he had changed his name and identity to Simon Green.