I agree turning in a family member for this type of a crime might be a stretch. But since you know what he is doing I'm sure there are others and it will be a matter of time before he does get caught and then if he is in dire straights with money he will be worse off. There has to be other means in which he can feed his family.
If more then the person commiting the crime knows about it, it's just a matter of time till he'll do the time.
Like I said before there has to be programs out there that can help him out. What about the rest of the family.
Hard to give a true oppinon about this without knowing the whole story, i.e... job, etc.