Step 1Heat the oven to 375 degrees. Clean the birds: Remove the little bag of neck, kidney and liver pieces (the liver will be used in this recipe, the rest can be saved for another use). Dice the liver and set aside. Place the birds on a rimmed baking sheet fitted with a roasting rack, and make shallow slits into the skin over the breasts of each bird, to allow the flavor to penetrate as the birds cook.
Step 2In a medium bowl, combine the brioche with the diced liver, diced bacon and apple. Season with one-fourth teaspoon salt and several grinds of black pepper. Stir in one-fourth teaspoon ground nutmeg, or to taste, and one-fourth teaspoon ground coriander. Add the orange zest. Remove the leaves from 2 sprigs each of the thyme, rosemary and marjoram, and stir them in with the stuffing (save the stems).
Step 3Brush the birds with the melted butter, and season each with 1 teaspoon salt, rubbing the salt over the inside and outside of the birds. Divide the stuffing and place half in each of the birds' cavities. Tie the birds' legs closed with butcher's twine to keep the stuffing from falling out.
Step 4In a large, heavy roasting pan, heat the grape seed oil over medium-high heat until hot. Add the shallots, carrots, celery stalk and remaining bacon slices, searing everything until golden brown, stirring frequently, about 15 minutes. Add the garlic and remaining herbs (and stems), including the bay leaves. Add the wine, scraping any flavoring from the bottom of the pan. Continue cooking until the wine is mostly reduced, then stir in the stock. Add the ducks and cover tightly with a lid or foil.
Step 5Place the roasting pan in the oven and cook the birds, 1 hour and 20 minutes for the geese and 1 hour for the ducks. Remove the lid and increase the temperature to 425 degrees. Continue to cook the birds, 45 minutes for the geese and 30 minutes for the ducks, basting every 15 minutes with the liquid in the pan.
Step 6Remove the pan from the oven and place the birds back on the rack on the rimmed baking sheet and place on the counter top to rest. Increase the oven temperature to 475 degrees. Cut the butcher's twine and untie the legs to remove the stuffing.
Step 7Strain the pan liquid (discard the vegetables and aromatics) into a clean pot, skimming and removing the fat from the top. Gently simmer until reduced by half. While the sauce is reducing, brush the birds with some of the skimmed fat and place them back in the oven to crisp the skin, approximately 30 minutes, brushing once or twice with fat (the fat should help to keep the skin from scorching, but keep an eye on it, tenting the birds if needed with foil).
Step 8Remove the crisped birds to rest a little while before serving. Serve the stuffing garnished with chopped parsley and the sauce served on the side.