Q: Can a brother give Zakat to his sister or Sadaqah would be more preferable
A: Zakat can be given to one's siblings provided they are deserving and eligible to receive Zakat. There is a double reward of assisting poor deserving family members with one's charities. One is for charity and the other for assisting one's extended family and maintaining ties with them.
And Allah Knows Best
Darul Ihsan Fatwa Dept.