Is it permissible to establish an ongoing charity (Sadaqa Jariyah) on behalf of oneself and one's sister while both are still alive?

Among the things that benefit a person after their death is ongoing charity (sadaqah jariyah), in accordance with the Prophet Muhammad's (peace be upon him) saying: "When a person dies, all their deeds cease except for three: an ongoing charity, knowledge from which others benefit, or a righteous child who prays for them." There is no objection to including others—whether living or deceased—in the reward of charity. Therefore, you can perform an ongoing charity on behalf of yourself and your sister.