Remove necks and giblets from hens; reserve for another use or discard. Rinse hens. In a large bowl, whisk beer, soy sauce, 1/2 cup brown sugar, molasses, garlic, ginger, dry mustard, and black pepper until well blended. Immerse hens in marinade; cover and chill at least 4 hours or up to 1 day, turning hens occasionally and submerging in liquid.
Meanwhile, in a 2 1/2- to 3-quart pan, combine orange juice concentrate, remaining 1/4 cup brown sugar, and the brandy. Bring mixture to a boil over medium-high heat and stir until sugar is dissolved, 2 to 4 minutes. Use warm or cool.
Lift hens from marinade (discard marinade) and set breast up in a 10- by 15-inch pan. Brush generously with orange-brandy glaze.
Bake in a 400° regular or convection oven, brushing every 10 minutes with glaze, until hens are richly browned and meat at breast and thigh bones is no longer pink (cut to test), 30 to 40 minutes. Transfer hens to a platter or plates and let stand in a warm place.
Meanwhile, skim and discard fat from pan juices. Add broth, cream, and remaining orange-brandy glaze to pan and stir often over medium-high heat, scraping up browned bits, until liquid is slightly thickened, 10 to 12 minutes. Pour into a small pitcher or bowl. Garnish hens with orange slices, if desired, and serve with pan juices.