Conversation so far:
Where did Olivier Messiaen grow up?
Olivier Messiaen was born on December 10 in 1908 at Avignon, France.
Who were Olivier Messiaen's parents?
Olivier Messiaen is the son of Cécile Sauvage, a poet, and Pierre Messiaen, a teacher of English.

Question: How many siblings did he have?
Self-contained rewrite: How many siblings did Olivier Messiaen have?