Answer:
(Fatwa: 1762/1378/L=1430)
(1 & 2) You are not responsible for the maintenance of your brother and sister except your parents, except that your brother or sister is too needy and it is difficult for him or her to survive. Therefore, if they are earning enough for their living, their expense is not wajib on you.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
