Here's whats going to happen. I'm not a legal expert but I know a lot of people that have been in trouble with the cops in cases like these.

Since he is 16 he'll be charged as a juvinile. His records will be sealed when he turns 18. He shouldn't be charged with vandalism, and the tesspassing charge is likely to be lowered to something like criminal mischeif. I don't know the laws in New York, but its very likely they aren't too much different than Tx. In the possession charge, He'll plea not guilty, and will be given a plea bargain. The prosecutor and his attorney will work out some kind of deal. It's likely that he will be charged with unlawful possession of marijuana, and be given probation. If he doesn't break his probation before he turns 18 his records will be sealed. If he does, he'll spend time in jail and those records will probably be held against him [even though legally, they aren't supposed to hold juvinile records against you as an adult, it is a witness of character.]

If he comes out of this without serving any time he needs to lay low and stay out of trouble for the next couple years.

All I can do is wish your brother the best of luck, and hope this serves as a little bit of a wake up call.