In a large stockpot over medium heat, melt the butter and add the oil, onions, pepper, parley, garlic, half of the cabbage, wine, salt, and pepper and cook until the cabbage starts to wilt, about 5 minutes. Reduce the heat to low.
Meanwhile, remove the crab legs from their packaging and lightly rinse with cold water, shake and set aside.
When all the crabs are cleaned, place the crab legs in the pot along with 1 cup of water. Stir the crabs around and add the second half of the shredded cabbage. Once the crabs and cabbage are well combined, cover the stockpot and raise the heat to medium. Cook the crabs until the meat is tender, about 15 minutes. Occasionally check the water level, which should increase as the crabs release their juices (but if this does not happen, just make sure there is enough water to continue to cook the crabs). Stir the pot well halfway through so that all the crab legs get a chance to cook directly in the liquid.