Diana has two older sisters. Sarah is the oldest and she actually introduced her little sister to Prince Charles back in the day. Sarah first dated the heir to the throne herself, but their relationship did not last very long. Soon after, Diana became the woman at his side.
Princess Diana's sister Jane also had a hand in her relationship with Charles. Jane was allegedly the one who convinced Charles to take his relationship with Diana public by taking her to a ball. Both sisters were part of the royal life at the palace and their children actually grew up with Prince William and Prince Harry.
Princess Diana's brother Charles is the 9th Earl of Spencer
Diana also had a brother who was born a year and a half before her, but little John Spencer actually passed away mere hours after his birth in 1960. Charles Spencer is Princess Diana's younger brother. The journalist is the 9th Earl of Spencer and the godson of Queen Elizabeth II.
After the death of his sister, he gave a moving speech at her funeral service. He criticized how the media had treated Princess Diana and promised to help raise her children in a more normal way without all the etiquette.
According to an Insider at the Daily Mail, the Queen and Prince Charles were really mad about his comments. Communication between Princess Diana's siblings and the royal family was reduced to a minimum in the following years.