Is zakat obligatory upon the eldest son who financially supports his parents and sister?

If the conditions for the obligation of Zakat are met, it becomes obligatory to pay it. What is spent on parents does not waive Zakat, nor is it permissible to count it as part of Zakat; because their maintenance is obligatory if they are poor, and it is not permissible to give Zakat to them. Similarly, the maintenance of a sister is obligatory according to some scholars, and in this case, it is not permissible to give Zakat to her, because it is a means of protecting one's wealth.