In a large stockpot, at least 8 quarts, place chicken carcasses in then put everything else around the chicken carcasses.
Fill the stockpot with water until the chicken carcasses are covered. Bring to a boil then reduce to an extremely gentle simmer (barely any bubbles) and let cook for 3 hours, uncovered. Stir occasionally.
After 3 hours, remove from heat. Let cool for 1 hour.
After 1 hour, remove the bones, as much as you can then place a large strainer over a large bowl and carefully pour contents of stockpot into the strainer.
Discard contents of the strainer then use a funnel and pour liquid into mason jars. Let sit at room temperature for a few hours then put in the fridge.
Read blog post for directions on freezing and also how long to keep in the fridge.
Notes
If you don't have bouquet garnis it's just typically dried thyme, dried parsley, black peppercorns, dried rosemary, and ground bay leaf. You can make your own by adding a teaspoon or so of each into cheesecloth and tying it at the top.