These locks are for your own protection against the foul creatures of the night. Your parents passed away, remember?
Your current guardian is this rich old guy. You haven’t bothered to learn his name, so you just call him gramps. You are not sure who the guardian of your sister is, however.
Your house isn’t well kept. It’s really old looking and spooky. If you ever get a hallucination or something you’d like to be in your locked room when it happens.