Place the chickens, onions, carrots, celery, parsnips, parsley, thyme, dill, garlic, and seasonings in a 16 to 20-quart stockpot.
Add 7-10 quarts of water and bring to a boil. Simmer, uncovered, for 4 hours.
Strain the entire contents of the pot through a colander and discard the solids. Chill the stock overnight.
The next day, remove the surface fat. Use immediately or pack in
containers and freeze for up to 3 months.