What is the best way for us to go about contributing to minors drinking charge against my son?

In the State of Indiana my 21 yr old son was charged with contributing to minors though he did not contribute any alcohol to the minors at all. He only had them pick him up from a party that he had been drinking from and he did know the minors had been drinking themselves until the he was already in vehicle and the minors started slurring their words. Officer arrested the 3 of them in a parking lot. One minor was only charged with public intoxication, the 2nd minor with DUI and underage drinking since he was the driver and my stepson with public intoxication and contributing to minor since the driver lied and said my stepson gave them the alcohol. This is my son's 2nd public intoxication. Should he plead guilty to both charges or should he get a lawyer to fight the contributing to minor charge since he is not guilty? I am mainly concerned about keeping him out of jail and the cost of getting a lawyer versus fines.