No. Steam purchases are tied to only one account. Separate accounts need separate installations of different purchases.
Steam Does allow you to share your games over your local network (think of this as the network in your house), but only one person can play the game: If you log onto your account and/or play the same game as your brother he may be bumped out of the game. You find the settings for this on your main Steam page under Settings>In-Home Streaming.