A court unlikely is responsible to verify the statements made under oath to the court. If a person swears under oath to tell the truth, then lies to the court, and there is no one to tell the court that the person is lying, the court has no way to discover the truth unless the lie involves something of which the court has personal knowledge. Once the court finds that the person is lying under oath, the court may do something to the person.
The third sibling may have a basis to ask the court to vacate or undo whatever court orders obtained by lying to the court.
The third sibling should promptly review the specific facts with the sibling's attorney. Delay in asking the court to do something may result in the court being unable to do anything.
"Left out" brother should engage a probate attorney, who should then file with Court & send a copy to the Personal Representative of a Notice of Appearance & Request for Special Notice &, after three months, send to the PR a Request for Copy of Inventory. Don't count on the Court --- the Court is not the "Probate Police" --- there is no "Probate Police." It's up to the left out brother to make & enforce his claim, which he should do through a probate attorney, preferably someone having some probate litigation experience.
You haven't mentioned it, but did the Decedent leave any living parent? If so, the living parent & none of the brothers is the lawful heir.
Richard Wills, WSBA 19720
That is an interesting question. The laws of the state in which the person died will more than likely indicate who is to receive the estate under the facts as you indicate. For example in the state of California, everything would go to the parents. In the event that the parents were not alive, then everything would go equally to the dead person's siblings.
In the event that the administrator of the estate (I presume one of the siblings) did not include a brother/sister, he would face serious consequences!