There is nothing wrong with the subscription so long as what is been watch is halal.
It’s your duty to make it clear to your brother that he should watch only what is halal or else you will stop the subscription or not allow him to use it . Otherwise, you will have share of the sin if he watches Haram. Your duty is to make it clear to them. As to whether they listen to it or not it’s not your duty. Your responsibility is to convey a clear message of your stand