选B,但home要加s.
all of whose homes 是非限定性定语从句,故用whose 替代their,也就是先行词the people,all of the people's homes,all of their homes.
例如：The children,two of whose fathers are scientists,were invited to talk about their families.
你的题中,两逗号间的内容是起补充说明的作用,叫定语从句,全句的主句是：The people were given help by the Red Cross,补充的是定语从句,all of their homes had been damaged by the flood.但做定语要用关系代词whose 替代their,以避免重复.