A section of the Wikipedia article discussing the culture of the Iroquois states the following:
...Since it was believed that the death of a family member also weakened the spiritual strength of the surviving family members, it was considered crucially important to replace the lost family member by providing a substitute who could be adopted or alternatively could be tortured to provide an outlet for the grief. Hence the "mourning wars".
One of the central features of traditional Iroquois life was the "mourning wars" when Haudenosaunee warriors would raid neighboring peoples in search of captives to replace those Haudenosaunee who had died.
The wiki article cites the following journal article:
War and Culture: The Iroquois Experience Daniel K. Richter The William and Mary Quarterly Vol. 40, No. 4 (Oct., 1983), pp. 528-559
Are there other examples of cultures who practiced ritual kidnapping as a replacement for specific individuals? If so, did they also torture the kidnapping victims?
Several citations available in this Wikipedia article https://en.wikipedia.org/wiki/Iroquois.