You must use "whose". You cannot use "which". whose = of which For all possessives you must use "whose".

The answer is yes. You may either one. But grammatical explanations would be different , and the stress in meaning is slightly different.

Eliot is right. I looked at it again. I think I took it at first sight for "where" which can be also used here to form a attributive clause. "whose" is possessive case of "who". So if you want to use "which", "in" needs to be added before it.