Roald Dahl had quite a few siblings, all of them girls.
His father's first wife sadly died leaving him with a son and a daughter to look after. It wasn't long after that though that he married his second wife, with which he had Roald, along with 3 other daughters.
All of these children were born in the space of 6 years!
Roald's four sisters were named named Astri, Alfhild and Else and Asta. His youngest sister Else was born in 1918, a few years after Roald, who was born in 1916.
Sadly Dahl's older sister, Astri, and his father both died in the same year, in 1920. Astri died of pneumonia at only 7 years old, and it was her death that led to his father also slowly deteriorating. However in this year Roald's younger sister Asta was also born.
There is actually a Roald Dahl museum where you can find out a lot more detailed facts about the writer.
As well as this there are many websites dedicated to giving information about his life, the most reliable of these being the official Roald Dahl site.
So this might be worth checking out!