Coming out to my brother?

So I'm going to come out to my family soon. My sister already knows, and she's pretty cool with it, but my brother doesn't know. He's younger than me, and i'm pretty sure he's already guessed, like my parents, but it really feels like it's different to come out to your siblings than to come out to your parents.

This is my depressed, sensitive brother who has always wanted a brother. (at least i'm ftm!) Me and him have always been close, but in a different way than my sister. Me and my sister are always talking to each other about all our problems and shit, but me and my brother play games together and roughhouse or just sit there and eat or watch a movie. He's smart, and like I said has probably already guessed, but I do sort of need to come out to him legitimately, like I need to do with my parents. Should I add his and my sister's (even though she already knows, i don't want to leave her out) names to the letter I write my parents, or should i tell him beforehand, or should i discuss it with my parents about how to come out to him or what...? I'm kind of at a loss, because this really feels different than my parents...

thanks