It is really a great story so far. What you need to do next is to write what did Ryker and Noelle do when they heard the footsteps above them. Did they investigate or did they leave the house? Since Ryker had already told Noelle that his brother was going to try and murder her, I don't think you should send them directly upstairs to see what or who made the footsteps. You should let the story continue a little more to be more dramatic. Don't let the story be a cliche like others would do. Perhaps, they could hide and wait to see who comes down. They could also catch the brother and then call the police or even the parents. You want the story to be different and have more excite to make the reader be wowed in the end.
The creepers in lord of the flies are actually vines that grow all over the island, which symbolize evil.
Such as when the pig is found entangled in creepers, it symbolizes how the boys will also become entangled in evil as they lose civility.
