Put half of the red grapes and half of the white grapes in the freezer, for garnish.
Put the remaining grapes in a large bowl and "smash" them with a whisk (or fingers).
Add the smashed grape to a large pitcher and pour in the grape juice and honey. Stir in about 16 ounces of vodka. Fill glasses about 1/2 full with the grape juice mixture and top with a splash of seltzer. Drop and few frozen grapes into each glass for a festive garnish that doubles as an ice cube!