10 plants isn't much from a growers point of view. Statistically half of them are going to be males so are useless, that leaves 5. Usually one of them ends up under par, so 4 good plants is a nice little grow. Nothing more.
But from the cops point of view one plant equals one pound so that's 10 pounds of pot right there. That makes it a major grow and your cousin a dealer.
The law is draconian.
The best thing that could help him is if it's his first offense.
Either way he needs a lawyer for sure. Do you know what state he's in?
EDIT:
Damn OP I just saw you got banned and why
...what did you do that for. That was a crazy and unnecessary thing to do!!!