To prepare simple syrup, microwave sugar and water in a microwave-safe liquid measuring cup until sugar is dissolved, about 2 minutes; set aside.Thinly slice two of the six oranges then place orange slices in the bottom of a large pitcher. Add mint sprigs and simple syrup.Use a cocktail muddler or the back of a wooden spoon to gently muddle the oranges with the mint and simple syrup help release all of the flavors.Add rum, orange blossom water and lime juice to the pitcher then stir.Fill four glasses with ice then fill ¾ way with mojito mixture. Top each glass with 4 ounces club soda to serve.