A short story by Serena Blade.
The basic idea of the story is sound, a solid foundation for a classic horror tale. The problem comes from too much detail being included. Much of what you tell the reader is irrelevant to the story and is better left out. Remember that a short story is meant to be just that - short. The reader expects that it will hold his attention for a brief while, provide a surprise at the end and be done with. It's our job to keep the interest up, make them care about the protagonist and then scare them or at least amuse them with an unexpected ending. It's a tall order and one we need to remember as we write.
The title is a little uninteresting. Doorstops are fairly mundane, after all. It's worth taking a bit of time to come up with a more intriguing name for the story. This particular one could be A Fishy Tale, for instance, or Cursed Dreams. Both make a reader ask questions they want answered. We are, in effect, giving them a brief glimpse of one aspect of the story, without giving anything away. To find out more, they have to start reading.
The basic story is simple enough but obscured somewhat by the wealth of detail included. For example, the cell phone doesn't work (which explains why they can't contact help) but it really doesn't matter why it doesn't work. Let the reader imagine a reason.
Don't feel that you have to explain everything that happens. This passage is an example of too much information: "To keep her mind from running wild she decided to walk around and explore the house. As she entered an office she found something that had caught her attention. Behind the door was an old Victorian antique doorstop. It was a brass mythical large fish."
We don't need to know why she explored the house. The important fact is that she did. Then we have three sentences that describe her discovery of the doorstop. Most of this can be deleted to give only the important information - In an office, she found a brass doorstop in the shape of a fish. The fact that it caught her attention is unnecessary as it wouldn't be mentioned if it hadn't caught her attention.
At the same time, you have to be careful to preserve the reader's belief in the story you're telling. You have said that they found a fully-furnished, open but deserted Victorian house in which to shelter. That requires at least a short explanation to explain why such a house should be abandoned and available to them. I know that was the question that arose immediately in my mind. Not many people leave a perfectly habitable house unlocked and open to squatters overnight.
Dialogue is our best chance to communicate character to the reader. Don't use it to get to the next action but as a way of revealing what your characters are like. My way of doing this is to put myself in their position and allow the character to speak through me. In my entry for today's contest, I imagined the proprietor as a typical old man surrounded by the ancient clocks of his shop. He is fussy, respectful of his customers and goes to some lengths to prevent the purchase of something that he feels can only lead to a bad outcome. This is all communicated through his conversation with Bernard. It doesn't need to be described - the reader will do it for me.
So put that dialogue to work!
Flow and pace is fine except for the previously mentioned detail scattered throughout the text. This is so much true that, when you start describing the history of Sita and Dimitro, it becomes confusing and I must admit that I began to skim. Essentially, it's an info dump and should be kept as short as possible so that the reader does not become distracted from the main story.
Consider rewriting the story in a rigidly chronological timeline (we really don't need to start with Jessie in a strange bed) but with an introductory piece recounting the tale of Sita and Dimitro, This would prevent the disruption of the tale being inserted in the middle of Jessie's story. It would also allow you to move straight to the transformation of Josh and Jessie into fishes, without bothering to free Dimitro and Sita from their curse.
I have written quite a lot about your story but do not become discouraged. Most if not all of my points are related to each other and, if you fix one, you will go at least some way to fixing others. Above all else, remember to keep the action moving - don't allow yourself to wander into descriptions that may matter to you but really don't help the story to progress. Keep it simple!