I think my mother has been abusing my siblings and I can't tell anyone
Well what is she doing to you all?
She has been hitting us when she feels like it.
I can understand why your siblings might be trying to hide the abuse when the abuser is your mother.  You should still tell someone, though, because abuse will have long-term effects on you and your sibling. Abuse is not tolerated and your mother should be held accountable.
I can't trust anyone besides my mother.
That is what you think, but it is definitely not the truth. You should tell someone that can help if you really are being abused by your parent.