If my brother sent his wife a picture of his penis and his wife sent it to my wife, can he be charged with a crime?

No. As an adult he can take pictures of his junk if he wants to. Even sending it to his own wife was OK if they are both fine with that. 

WHY would your wives be exchanging pictures of his junk is one question YOU need to get  an answer to. Why would your wife want a picture of his, and what would have motivated his wife to send it to her?

That's absurd. Your issue is with your sister-in-law and her impropriety. None of you sounds mature enough to be married. 

There aren't penis crimes out there.  

No he cant, but his wife can be charged. But you need to make your brother aware of what she did,

His wife could be committing a crime because she sent his picture to someone else without his permission. Think of it as the guy being the photographer so he owns the rights to that picture.