Legal Question in Criminal Law in Washington

What ethical issues my arise if a lawyer answers a student's homework for her so that she never masters the material?

Way too little information for such a potentially important question. There are certainly situations where the Washington rules of ethics are not violated by such representation. But a written notice of potential conflicts absolutely has to be in the file, for each client. If there is ANY conceivable way the defendants could present inconsistent defenses, there is no good reason to try and represent both.

In my opinion, there is never a good reason to try and represent two co defendants in any case, regardless of their relationship. Each client deserves independent advice.