Toss together sweet potatoes, oranges, onions, butter, oil, and salt and pepper to taste.
Put a 2-foot-long double layer of foil on a work surface. Place half of sweet potato mixture in center and sprinkle with 1/2 cup raisins. Cover with a third sheet of foil and tightly roll up all sides to seal. Wrap packet in a fourth sheet of foil to ensure insulation. Make another packet with remaining vegetables and raisins.
Put packets side by side directly on hot coals. Cover grill and open grill vents, then grill packets until vegetables are tender, about 30 minutes.
While packets are grilling, stir together honey, lemon juice, and parsley. Remove packets from grill and carefully unwrap. Drizzle vegetables with honey mixture.
Cooks' notes: Gas grill method: Put packets on grill rack and close lid. Roast with grill set to moderately low.
Oven method: Toss potatoes, oranges, onions, raisins, butter, and oil together in a large shallow roasting pan. Cover tightly with foil and roast in a preheated 450°F oven until potatoes begin to soften, about 50 minutes. Uncover and roast until vegetables are browned in spots and tender, about 25 minutes more.