Mix ground beef, 1/4 pound tomatillos, eggs, white rice, 3 cloves garlic, 1 teaspoon cumin, and 1 teaspoon salt in a large bowl.
Scoop 1 1/2 tablespoon of the beef mixture and roll into a meatball. Repeat with remaining beef mixture.
Combine tomatoes, 1 onion, 3/4 pound tomatillos, chipotle peppers, and 3 cloves garlic in a blender; puree until smooth.
Heat oil in a large pot over medium heat. Add tomato puree; cook and stir for 3 minutes. Pour in chicken broth. Season broth with salt and pepper. Bring to a slow boil; reduce heat until broth is barely bubbling.
Lower meatballs carefully into the hot broth; simmer gently for 20 minutes. Add remaining 2 onions, carrots, celery, cilantro, and 1 teaspoon cumin. Simmer until rice in the meatballs is cooked through, about 1 hour and 15 minutes.
Squeeze some lemon juice into each bowl. Serve with corn tortillas.