When my husband was a bishop in our church, he counseled a lot of college youth. One thing he found was that college age kids who came from homes where they didn't have experience choosing good things because parents controlled everything they watched and listened to, had a lot of trouble with self-control when they left home. They just didn't have the experience needed to stay safe in a digital world.
So we decided after that to teach our teens self-control. We can't be everywhere with our teens. They are going to have opportunities to do things we don't agree with and that might be harmful to them. So we spend a lot of time educating them about choices and consequences during our family night and during family dinner, and also as we drive them places. We don't always lecture, we try to make it a discussion so the teens can apply what they are learning in their every day lives.
This method has worked really well. My teens seem to be gaining practice and experience in controlling themselves with media, and if they make mistakes, we talk to them right away about how they feel about it, and what they can do to not have harmful consequences. If we have accidentally given them too much freedom, too early, before they are mature enough to handle it, we go back and take control until they are mature enough to handle it.
Another thing is, we try to let teens have control in things that don't matter, such as how they wear their hair. If they want to get a mohawk, we let them. If they want to eat 5 donuts and get sick...we let them try that. It usually only happens once. This is because teens will try to express their individuality and experiment, and it is better if they experiment on things that won't harm them. Let them find out that their parents were right, and they shouldn't have procrastinated that school project so much. This will improve your credibility and they will learn faster. But always be teaching along the way and offering support...not taking away their consequences, but telling them you love them. You can ask them how they can do better in the future. Remember that different children will be more or less mature and you will have to gauge how to treat each one individually according to their maturity.
Because we let teens have control in things that don't matter, it gives us the leeway to control in things that ARE harmful. We give them strong boundaries against truly harmful things. For instance, we don't let our kids go to parties with alcohol or drugs. We teach that being around that kind of thing over time will break down their resistance and they will eventually succumb to peer pressure. We don't let our kids look at pornography because we teach that it is harmful and addictive. We also don't let them go to rated R movies, and we teach that they need to make sure the PG13's aren't harmful before they watch them, though we let them choose what PG13's they watch, so they can gain experience. We let our children choose what they wear, but we teach strongly that they need to be modest to avoid serious consequences in attracting the wrong kind of attention. If my daughter chooses something questionable, usually I teach some more and she decides to wear something else. Because I have spent a lot of time loving her, with the 5 love languages, she listens to me. So you have to take a look at your own personal and family standards and see what to control and not control, and what you think will be harmful, and what doesn't matter.
One last note...children won't care how much you know until they know how much you care. So keep giving them those love languages, so that they are ready and willing to listen to you when you teach.
I hope this helps your family. It is definitely something you have to constantly work on and watch over. But given experience under your watchful eye, your teens should be ready to control themselves better once they leave home.