I would think you need a buy-in from these kids that they agree these influences are harmful and that they don't want it in their lives or at least moderated it. Otherwise it's an uphill battle to regulate those influences.
Buy in is nice, but parenting does not require buy in on your rules, just a clear understanding and explanation of your role, and why the roles of parent and child and the rules that sprout from that relationship exist.
To me, buy in is necessary, especially when they will eventually become adults and free to make their own decision and it will be much harder for them to control their addiction especially when there is no more guardrail or when you no longer have authority. We're raising them to be autonomous adults, after all.
