Hmm, with how honest the siblings are presenting themselves yet onee-chan still thinks she can win, are we getting a bunch of lies? Could be interesting if the bracelet was a transformation item rather than directly disease halting (transform into healthy body), and the deciple isn't actually onee-chan but little sibling transformed into her making onee's kind actions all actually pure. Then the true plan to break the party up was meant to be them abandoning the sibling like they suggested, and the guilt while facing pure hearted onee-chan's rage that they sacrificed a child (who presumably just transforms into someone else and leaves)