Cut oranges into 1/8-inch slices, discarding ends.
Cut slices into quarters.
Layer one-third of orange slices, one-third of cranberries, and 1 cup sugar in a large bowl. Repeat procedure twice with remaining fruit and sugar. Cover and let stand 8 hours.
Bring orange mixture and orange juice to a boil in a Dutch oven; boil, stirring constantly, until sugar dissolves. Pack hot fruit into jars, filling to 1/2 inch from top.
Add 2 tablespoons brandy to each jar, if desired. Cover fruit with boiling syrup, filling to 1/2 inch from top.
Remove air bubbles; wipe jar rims. Cover at once with metal lids; screw on bands.
