The uppermoons are doing training by which Muzan taught it would make them stronger, Kokushibo's training is using techniques and after this training is the 'final battle' with him, as for some of the uppermoons have quite a hard time doing this- Muzan sometimes watches Kokushibo train them or he's not there, pick who you want to be then we may begin!

1: Muzan 2: Kokushibo 3: Doma 4: Akaza 5: Nakime 6: Hantengu 7: Gyokko 8: Daki 9: Gyutaro 10: Kaigaku