"our (singular)" in French

“Notre” agrees in number with the noun that follows, not with the number of people talking. It is the same in both masculine and feminine forms. e.g.:

Léa and Tom say: Notre frère s’appelle Jerry.  (“Our brother is called Jerry.”), because brother (frère) is a singular word.

Tom and Jerry reply: Notre sœur s’appelle Léa. (“Our sister is called Léa.”) because sister (sœur)  is a singular word.