Does sharing in the payment of the internet bill with siblings who use it for forbidden matters, such as songs and movies, make me sinful, knowing that I use it for knowledge and benefiting from lectures? And what is the solution if I am denied internet access due to not participating in the payment?

Do not share with your siblings in paying the internet bill if they use it for what Allah has forbidden. The internet can be replaced with ready-made programs and CDs. If you need something that can only be found via the internet, you can seek help from some colleagues who have access to this service.