They barely accommodate that number of persons and no more. A six passenger limousine can accommodate six people, not seven. If you are preparing directions for your guests, please send a copy to your limousine company. The use of alcoholic beverages is not legal in most locations. This is particularly true for proms, where state inspectors frequently stop and search limousines for contraband alcohol.
Most states stringently enforce limousine licensing.
In many places, the vehicle can be stopped and immediately impounded if not in compliance. Make sure your limousine company is licensed and insured.