بسم الله الرحمن الرحيم
(1) You should inspect by other means and if he is illegible for zakah then you may give him zakah, otherwise not. The holy Quran says:
إِنَّمَا الصَّدَقَاتُ لِلْفُقَرَاء الآية [التوبة : 60]
(2) When your sister is sahib nisab then it is not lawful to give her zakah. And if her husband owns business goods more than nisab then it shall also not be lawful to give him zakah. However, you may support your sister and her husband by imdad money, it is lawful.
Allah knows Best!
Darul Uloom Deoband