Place potatoes and eggs in cold, salted water. Bring to boil and reduce heat to simmer. After 12 minutes remove eggs from water. Peel and chop while potatoes cook for additional 3 minutes. Drain water off potatoes and let cool slightly.
In extra large bowl, stir together mayonnaise, mustard, dill, pickle relish, onion, scallions, parsley, and lemon juice. Taste and adjust accordingly.
Add diced potatoes and chopped eggs into mayonnaise mixture. Toss to coat. Salt and pepper to taste. Refrigerate overnight, or @ least several hours.