If you’re using dry breadcrumbs, soak them in milk first like others suggested. Also, go down to two eggs and consider ditching the onion soup mix. It’s adding a lot of stuff you don’t need plus a buttload of sodium and preservatives.
My meatball recipe: One pound ground beef or meatloaf mix, one cup fresh breadcrumbs (or dry soaked in a bit of milk), one egg, one clove of garlic (minced), one tablespoon minced fresh parsley, one tablespoon grated parmesan cheese, salt and pepper to taste. Mix gently, form into balls, put them into a pot of simmering marinara sauce, cover, and simmer for at least 30 minutes or until cooked through. They will melt in your mouth. My husband’s family is Italian and they rave over these meatballs. Also, the sauce will take on a wonderful flavor from the meatballs.