Formal:
* A deux frères. (This is the most literal translation and works in most situations.)
* Il a deux frères. (This is the most common and natural way to say it.)
Informal:
* Il a deux grands frères. (This emphasizes that they are older brothers.)
* Il a deux petits frères. (This emphasizes that they are younger brothers.)
Using "avoir" with a possessive pronoun:
* Il a ses deux frères. (This emphasizes that the person has "his" two brothers)
Remember to conjugate the verb "avoir" correctly depending on the subject of the sentence.