Place potatoes into a large pot and cover with salted water. Bring to a boil then reduce heat and simmer until tender, about 15-20 minutes.
Drain potatoes, then transfer them to a large bowl and mash with a potato masher.
Stir in onion, eggs, celery, pickles, salt, parsley, and pepper into the mashed potatoes.
Mix mayonnaise, sour cream, 2 tablespoons of pickle juice, and mustard together in a separate bowl; pour over potatoes and mix until well combined. Adjust seasonings and add more pickle juice if needed.
Cover and refrigerate for at least 1 hour before serving. Sprinkle with paprika for garnish when serving.