The tale of the three brothers and their little sister

Many had said there were only the Peverall brothers. But what if that was not true? What if there was a sister named Callista? And what when Death offered congratualtions and gifts if she asked for something astounding, that nobody would ever think of? Read to find out. (I do not own Harry Potter. But I do own Callista Peverall. Also ask for update if you wish there to be one.)