My mom recently passed. She lived alone. We cannot find the will. I have two siblings, of 8, that are going into Mom's house and helping themselves to her belongings and paperwork.
This is super wrong. They are looting your mother's house. None of these things belong to them, at least not yet.
You will need to find legal help quickly. Laws differ depending on your state. Unfortunately, you may not get all these things back since you don't know what's been taken.
I'm sorry you are having to go through this.
You might consider installing new locks on the doors now to stop your siblings entrance.
It's called Dying Intestate...which means without a will. In that case, the state handles her final affairs. Change the locks and get an attorney.