To make the broth, pour the water into a stockpot and add about a tablespoon of salt and both grouse. Bring to a simmer over medium heat. Once the water simmers, turn the heat down below a simmer. You want it steaming, but not bubbling.
Let the grouse cook for 30 minutes, then pull them out. Strip off all the breast meat and set aside. Return the rest of the grouse to the pot and continue to cook for another 30 minutes to 1 hour. Pull the birds out again and strip off all the remaining meat. Set aside all the grouse meat into a container and return the bones to the pot. Cook for another hour or two.
Add the remaining broth ingredients and bring everything to a simmer again. Simmer this gently -- the water should just barely be bubbling -- for another hour. Turn off the heat. Set up a fine-meshed sieve over another large pot or bowl and put a piece of paper towel into it. Pour the broth through the paper towel-lined sieve into the other container. You might need to stop and switch paper towels if it gets too gunked up. This broth can be stored for up to a week in the fridge.
To make the soup, cover the rye berries with enough water to submerge them by 2 inches. Add a healthy pinch of salt and boil until tender. (This can also be done in advance.) Meanwhile, set a large pot over medium-high heat and add the butter. Once the butter is good and hot, add the sliced onion and saute until it is translucent but not browned, about 3 to 5 minutes.
Pour the broth over the onions and add the sliced carrots. Heat the broth to the steaming point. By the time the rye or barley is cooked, the carrots in the broth should be, too. Add the peas and the reserved grouse meat to the broth and cook for another three or four minutes. Add the smoked salt to taste.
To serve the soup, drain the rye berries and divide them among individual bowls. Ladle the soup over the grain. Garnish with paper thin slices of radish and chopped parsley.
The broth can be made several days in advance and stored in the fridge.