First and foremost, take a deep breath and relax. They're not in that much trouble.
You should simply consult a criminal defense attorney in practices in the New Orleans area as soon as possible.
Most minor in possession ("MIP") cases rarely ever result in a conviction. Rather, the New Orleans City Attorney's Office usually offers a "diversion" program, where the defendant(s) can complete the requirements where you live. In fact, if you retain an attorney in a timely fashion, he or she could handle the entire thing without you ever having to drive back to New Orleans, upon the execution of the proper documentation (thereby saving you the trouble and expense of having to travel back to New Orleans). Once the diversion program is successfully completed, the case is dismissed and the entire matter can be expunged from their record.
But, don't be stupid. While a skilled criminal defense attorney can guide a client through this without a conviction, the MIP statute actually has some teeth to it (e.g.- a conviction can actually result in the suspension of your driving privileges and 6 months at parish prison). So, while they probably just received a ticket or summons, they have actually been charged with a misdemeanor offense.
Best of luck to you!
The important thing is to contact and retain an attorney as soon as possible and let he or she handle it.