Mariah Carey is known for her diva-ish excess. But — if it's true — what's going on between the singer and her siblings seems way beyond the bounds of her normal character.Morgan Carey, the eldest of the three siblings, is claiming that Mariah refuses to contribute to their dying sister's hospital bills. Alison Carey — a reported former prostitute from New York City — is HIV positive. She is slated to undergo brain and spinal surgery in what Morgan is intimating could be a lifesaving treatment."Your sister is dying and she is struggling and where are you?" Morgan appealed to his famous sister, speaking to The Sun. "You think you are so fabulous, but you are a witch.”"Mariah needs to step up," he added. "I flew in from Hawaii last year when Alison was taken off a ventilator, believing she was going to die." He also said that Alison has reached out to Mariah throughout her illness and has not received communication in kind.So is Mariah really behaving cruelly, or is Morgan blowing this out of proportion? It's hard to tell — reports are coming from The Sun, after all. But — either way — hopefully Alison is getting the treatment she needs.