|This was an interesting start to what promises to be an intriguing story of mystery and horror. I do have a few pieces of advice which may help you further grasp the reader's attention.
1. I suggest you be more vague with how Carter obtained the four girls in the prologue and allow flashbacks throughout the story tell the full tale of how they became his powerful little group. For example...
In the third paragraph, you spoke of how Carter obtained Alyssia. I humbly suggest that instead of going into detail, you merely state that he was forced to make Alyssia and her older sister orphans that night as their parents were less than cooperative.
2. Also, in the third paragraph, you may wish to give a reason why he spared Ayssia's elder sister who could be a key witness for the police to build a case against him. I suggest this: He spared the elder sister as she showed promise to be useful at a later time. He had someone else acquire her to be held until a time of his choosing: This would close any plot holes that would raise questions later.
3. In the fourth paragraph, you stated that Adria's parents practically threw her out with a suitcase of money. I humbly suggest you change that so he arrives just as she is being thrown out with the money and he offers to take her in. She accepts, sobbing at the fact her parents abandoned her.
4. In the eighth paragraph, you stated that Adria reacted the most negatively against the fusing of a demon's soul while Julia was easier with an angel's soul. You might wish to add, :In retrospect, it might have been more productive to have given Adria the angel's soul instead. Too late now...:
5. In the first to the last paragraph, you stated that Carter was blackmailing Alyssia's older sister since he murdered their parents. This will raise questions such as what does he have over her and why would she care as he killed her parents? I humbly suggest you state that he had been using the well being of Alyssia's elder sister as a tool to keep her loyal. For example: She does well, her older sister is treated well.
Overall, this was a fine prologue. I found no spelling or grammar mistakes and it flowed nicely. I hope my suggestions help make your story even more intriguing.