Grilled Cornish Game Hens with Lemon, Sumac, and Date Relish

Name: Grilled Cornish Game Hens with Lemon, Sumac, and Date Relish
Yield: Makes about 8 Servings
Ingredients: 9 cups water; 1 cup fresh lemon juice, divided; 1/2 cup coarse kosher salt; 5 1-1/4- to 1-1/2-pound Cornish game hens, cut lengthwise in half, backbone removed; 1/2 cup olive oil; 2 tablespoons ground sumac*; 4 garlic cloves, peeled; 10 very thin lemon slices; Date Relish