Formal:
* Votre frère n'est pas à la maison. (This is the most literal and formal translation.)
Informal:
* Ton frère n'est pas là. (This is a more casual and direct way to say it.)
* Ton frère est pas à la maison. (This is a more colloquial version of the formal translation.)
You could also specify the reason:
* Votre frère est parti. (Your brother is gone.)
* Votre frère est sorti. (Your brother went out.)
* Votre frère est au travail. (Your brother is at work.)
Remember to use the correct pronoun (your brother) based on the context. "Votre" is used for "your" in a formal context, while "ton" is used in an informal context.