Well, he can't really complain if you (or your husband) bring it up, since he effectively invited you to peruse his myspace page. Crass language, etc., is pretty typical for a 13-year-old boy who is within a circle of similarly aged boys... but the drinking is certainly something that needs to be dealt with.
I suspect by inviting his older sister to peruse the site, the younger brother was asking for implied endorsement of the things therein. If she does not object to these things, he can be forgiven for thinking that his sister considers the drinking and such to be "cool", and not a problem.
The little brother has really put his sister in a difficult position. She should not feel too guilty if his toes are stepped on as a result.
Plus, binge drinking in a 13-year-old is the express ticket to alcoholism. A kid does not have a clue on how to handle alcohol. The same can be said of some adults, but it is true of just about every 13-year-old. Somebody needs to intervene.