I feel really uncomfortable in my own house? Please help!?

No wonder you don't feel comfortable! Strangers are just breezing in like it's the public park. Is the house your brother's? If so, there's not much you can do. If your parents own the house, you should talk to your brother first and tell him you don't feel comfortable with these people roaming around. If that doesn't work, then you should speak to your parents about it.