is this also incorrect because "whose" can only be a pronoun for a group of persons, not objects such as branches? If so, what pronoun can one use?
No, whose can be used with non-person items.
Here is what the dictionary has to say about this: Sometimes the phrase of which is used as the possessive of which: Chicago is a city of
which the attractions are many or Chicago is a
city the attractions of which are many. The use of
this phrase can often seem awkward or pretentious,
whereas WHOSE sounds more idiomatic: Chicago is a
city whose attractions are many.