4.He's a man from whom we should learn. = He's a man (whom/who/that) we should learn from.
比较：He is the student whom you think to be worthy of your praise.
He is the student who you think is worth praising.
5. A child whose parents are dead is called an orphan.(指人)
I'd like a room whose window faces south. (指物)=I'd like a room of which the window faces south. =I'd like a room the window of which faces south.
There is a teapot shaped like a Chinese duck, out of whose mouth tea is supposed to come