Must teens help their parents to bring up their sisters or brothers?

On the one hand they must because they must help their parents.

But on the other hand may be teen didn't want another child in their family, but it was born. So why he or she must be responsible about this child in the future?

As for me, I think teens must help their parents and more than that when you grow up who will be the most close person to you? Only your brother or sister who you have treated like you like? Have you ever thought about it?