In my experience, college students are treated as adult non-house-owners. They don’t have a curfew, but they are expected to offer the basic courtesy of letting someone in the house know when to expect them to be gone or to come home. This is true whether you are 24 or 74. If you’re going to be gone until Monday, you say so. If you expect you’ll be out late, you say so. If your plans change, you send a text or make a call to say so. You are not required to say where you are or who you are with, but you do keep the rest of the household up on when you’ll be home and when you won’t.
Adult non-house-owners don’t have the ultimate decision-making authority of the homeowner, but they are usually afforded the courtesy of having their (name removed by moderator)ut considered as the (name removed by moderator)ut of an adult. They help around the house like an adult. If they’re a student, they usually get the chores that fit best around a student’s schedule, but they take some of the load of maintaining the house and getting the meals on the table. They do their own laundry and they pick up after themselves, leaving the common areas presentable when they leave them. They check with their housemates before inviting guests over, and they see to it that their guests follow the house rules. They introduce their guests to those living in the house and don’t expect to entertain guests in privacy (although their housemates may elect to give them that on occasion, if they are so inclined).
For instance, once I rented a room in a home owned by a non-relative. My work contribution was to wash the windows on a six-week rotating basis and to provide one meal each week. If I wasn’t going to be around, I could have a casserole and a salad ready in the refrigerator, but I got to do some of the cooking and shopping. The other rule was: If you don’t have time to clean the kitchen, your dinnerware, and any other mess when you’re done eating, you do not have time to eat.
In other words, make them act as if they were renting a house with someone their own age, only they weren’t the one who held the lease and ran the place.