Is it permissible to charge a laptop knowing that some family members will listen to music with that laptop once it is charged? Does this constitute helping in sin?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

If you are only charging this battery in order to use your device in what you need of permissible matters, then there is nothing wrong with that, even if it is used by others in what is not permissible, because the Shariah does not command you to delay what is in your interest for fear of someone else committing a Shariah violation.

However, you should advise those who use the laptop about what is forbidden and clarify to them that what they are doing is prohibited and that they expose themselves to the Wrath of Allah. Please, refer to fatwa 81545.

Nevertheless, if you only charge it so that it may be used by them in what is forbidden, then this is helping them in sin; Allah says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression.} [Quran 5:2]

Allah knows best.