Here's how you ask about brothers, sisters and other family in French.

The phrases covered are:

Do you have any children? - Vous avez des enfants?
I have no children. - Je n'ai pas d'enfants.
I have a son. - J'ai un fils.
I have two sons. - J'ai deux fils.
I have a daughter. - J'ai une fille.
Do you have any brothers or sisters? - Vous avez des frères ou des sœurs?
I have one brother. - J'ai un frère.
I have two sisters. - J'ai deux sœurs.
I have three brothers. - J'ai trois frères.
I have four sisters. - J'ai quatre sœurs.

This video comes from the Lexicogs Getting Started in French course.

To practise these examples, please visit:
https://lexicogs.com/how-many-brothers-or-sisters-do-you-have-french-examples/