Steep the tea bags in 4 cups of boiling water for 10 minutes.
Dissolve the sugar with the remaining 1 cup water in a 9X13" baking dish or other oblong baking dish or casserole dish (see note). Stir in the lemon juice and orange juice concentrate. Add the tea and brandy and stir until everything is dissolved and well mixed.
Cover the dish with plastic or a lid and place in the freezer. Freeze until solid, at least 4 hours or overnight.
Scrape the mixture out of the dish with a fork (it will be flaky and resemble a granita). Transfer to a blender (see note). Blend until the mixture is slushie, stopping the blender to stir/scrape down the sides as needed.
Scoop about 1/2 to 3/4 cup of the mixture into a short glass. Top with chilled sparkling water or lemon-lime soda. Garnish with maraschino cherries, a spoonful of maraschino cherry juice, and/or lemon and/or orange slices as desired.
Store any remaining slush in an airtight container in the freezer. It will remain at a scoopable consistency for future cocktails.
Notes
Use sparkling water or club soda to top your brandy slush with if you like your cocktails less sweet. If you like your drinks sweet, use lemon-lime soda like Sprite or 7-Up instead.If you find your baking dish or casserole dish is very full, pour some of the mixture into a second dish to avoid overflow while freezing. Depending on the size of your blender, you may also need to blend it two separate batches.