بسم الله الرحمن الرحيم
(1) Your sister cannot give her zakah to her husband even though he is eligible to receive zakah.
(2) If your bahnoi is eligible to receive zakah then you may give your zakah to your bahnoi and after being its owner and taking it into his possession if he invests it in his business then too your zakah will be paid.
(3) When you give your zakah to your bahnoi then after taking into his possession he will be its owner and it shall be lawful for him to spend it anywhere. If he spends this money on his family members then too there is no harm. Zakah is wajib on your sister. However, if your bahnoi spends it after taking into his possession on his wife then too there is no harm.
Note: Your bahonoi’s father is sole owner of his property during his lifetime and only he has all the rights. His children have no rights in his property. However, after his death all his leftover property will become his inheritance which will be distributed among his legal heirs as per Shariah rules.
Allah knows Best!
Darul Uloom Deoband