"whose were" is correct and usable in written English.
You can use it when asking who something belongs to. For example, "Whose were the shoes in the hallway?".
The sampling comprises 160 students whose were studying at 10th and 11th grades of seven different high schools in Turkey.
DNA tests will be done to determine whose remains were buried in Missouri and whose were left behind.
This paper presents new design of total hip endoprosthesis, elements of whose were developed from the standpoint of system analysis and synthesis of biomechanical objects and devices.
Its most loyal subjects — often people whose were most devastated by the war with Iraq — received favorable treatment, while the system's dissenters were quashed by execution, imprisonment or exile.
The French won the World Cup with the "rainbow team", a talented and committed squad made up of players whose were themselves born (or were sons of parents born) in all corners of the Francophone world and beyond.
His ancestors were not all American (whose were?), and it makes him un-American; similarly, Ralph Miliband's leftism is deemed more suspicious because it is tied to his foreignness.
