"I use my brother's machine."

Translation: Uso la macchina di mio fratello.

[Viaggiatore]

You would say "del mio fratello", but you don't say that either since you don't need the article with possessives involving close relatives. http://italian.about.com/library/fare/blfare124a.htm

[Ispirac]

I did that mistake with "del mio fratello". I forgot the rule about that.

[mardelnorte]

i am very confused in which cases we use "il", In this case I thought it would be fine to say "uso la macchina di il mil frattelo" by apparently it is wrong