Place the beef bones and oxtails in a large stockpot, cover with water. Bring the liquid up to a boil and cook for 10 minutes. Remove from the heat and drain. Rinse the pot and bones. Return the bones to the pot and cover with 6 quarts of water. Bring the liquid up to a boil and skim often to remove the foam. When the foam stops rising to the surface, add 3 quarts of water and return to a boil. Char the onions, shallots, and ginger, directly over a gas burner or under the broiler, about 5 to 6 minutes. Tie the charred vegetables, star anise, garlic cloves, and cinnamon stick in a damped cheesecloth. Add the spice bag and parsnips to the simmering broth. Season the broth with salt and pepper. Simmer the liquid for 1 hour. Add the tripe and tendons to the broth and simmer uncovered for 5 hours. Two hours after adding the tripe, add the flank steak and brisket.
In a small bowl, combine the green onions, cilantro and onions together. Season the vegetables with salt and pepper. When the broth is ready, remove and discard the oxtails and bones. Reserve the tripe, flank steak, and brisket. Strain the broth into a clean pot through a strainer with a double layer of dampened cheesecloth. Add the fish sauce to the broth. Bring to a boil and reduce to a simmer. Slice the tripe, flank steak, and brisket, into small pieces. In a pot of boiling water, drop in the drained noodles and remove immediately and drain. Mound the noodles in the center of an oversized bowl. Bring the broth to a rolling boil and ladle the broth over the noodles Arrange the remaining ingredients on small plates around the bowl of broth.