My Book Synopsis

I'm curious to get some feedback on my upcoming horror novella.
(Keep in mind this is still a work-in-progress)

The novella is set in London, England from the years 1795 to 1826
Basically it is being written in three sections, each part telling the story of a member of the Harrington Family and their interaction with two vampires.

The entire book is being written as diary entries.

Here are some examples:

August 13, 1795.

There is evil in this world. I can no longer deny that fact, for I have seen its face and heard its voice.
But evil is not repellent to me, as it should be. No, it is great temptation, a banquet of all I have wanted in this life. If I give over my soul. I should be afraid of this, I should flee from all thought of what I am contemplating. Why do I not?
A lifetime of belief is being undone by temptation. I have always done as I was taught. I have always trusted in God, but now I consider rejecting Him. Why? Perhaps my faith was not as strong as I believed.

August 17, 1795.

I talked to Henri regarding my doubts. He told me it must be my choice. I must choose between my beliefs and morals, and my desires. To that I will admit upon these pages, if no where else. For what I must do is selfish, even cruel, and will ruin utterly the life I live at this moment. To make the choice will take me into the shadow.