Soak all the bones & oxtail in cold water for about an hour. Soak the oxtail and bones in separate bowls. Add 2 tsp sugar to each bowl to speed up the soaking process. Change to clean water 3-4x within the hour. Rinse oxtail bones 3x and set it aside. Rinse LA Galbi beef bones 10x or until no more particles come out and water runs clear.
Bring 10 cups of water to boil in a large pot. Parboil the bones and oxtail together for 5 min. Discard water. Rinse meat/bone in cold water 3-4x. Set in strainer.
Trim fat off the oxtail with scissors or knife.
Add to the Instant Pot, 9 cups of water and LA Galbi bones. Seal and Pressure cook high for 2-1/2 hours. Quick release the vent. Skim the floating fat.
Keep the bones remaining in the pot. Add oxtail, radish, scallion, onion, garlic, whole peppercorns. Select Pressure Cook on high for 45min. Natural release 15min. Release valve. Discard all aromatics but save the radish. Cut radish into big chunks for serving. Skim floating fat.
Boil handful of dang myun/Korean vermicelli (sweet potato noodles) per the package until soft. Rinse and set aside for later. Chop Scallions, set aside.
In a big soup bowl, add oxtail, sliced radish, dang myun, and pour the broth on top. Sprinkle chopped scallions. Serve salt and pepper in a separate bowls.