Do I need a laywer to go to court with us for his hearing

My son who is from Fl is 17yrs old, he went to stay for a week in SC with my neece who is 20yrs old, they were stopped for expired tags, my neeces car. They found a dime bag of pot and they were arrested in Walterborr, SC. When they asked my neece if it was hers she said no, when they asked my son he said no..but is was my sons..they were both arrested and made bail..when my son goes back for a court hearing if he tells the judge it was his , will the charges be lessoned for my neece? It was a first offfense for both.