I'd respect Jake's silence. When he's again communicating, then would be the time to follow his lead and react accordingly, based on what he's saying. Until then we know Jake is part of a tight and loving family circle. He isn't alone. Let him grieve in peace.
This is what I will probably do (figuring that Jake's family should be particularly sensitive - after all, Jake's sister has also acted with Heath, and Jake's parents are in the entertainment industry).
But sending cards via Jake's agent probably wouldn't be too intrusive. If Jake doesn't want to hear from fans yet, his agent can hold onto the messages until Jake's ready for them. So if people want to send condolences to Jake (or to Michelle, for that matter), there's a way to do it without being rude.
(The paparazzi and the entertainment magazines, however, should leave Jake alone until he's ready to talk to them. That includes People, whether the story from the unnamed source on the set of
Brothers was true or not. The magazines are feeding their own profits, and feeding the curiosity of the fans; they aren't doing anything for the sake of Jake's grief. And yes, I'm aware that I'm focusing the anger stage on the entertainment media...)