When Jacob enters his fathers house after his funeral he finds the knife his father took his own life with. Both the knife and the carpet in the room where the death happened are covered in fresh blood. Since the funeral took place at least one, possibly more days after his fathers death there neither wouldn't be fresh blood stains nor the knife itself. It'd be a crime scene and therefore totally occupied by the police.
The Eloise didn't close in 1982. The asylum officially closed in 1981, but the patients had all been moved out by 1979.
The Eloise hospital complex was off limits to the public from its closure in 1981 till late 2018. Nobody could go there to request records, and no lawyer would tell them to.
There was no fire at the Eloise.
Neither the asylum nor the hospital closed down because of the damage from a fire that didn't happen.
There are photos of the interior of the buildings from 2018 showing the only damage is from time and vandalism. The highly offensive and widely protested haunted house attraction opened in the buildings relied on the hospital being intact, with much of the original furnished, fixtures and fitting remaining for the actors to interact with.
Although, as of 2024, very little of the original hospital remains, having been "improved" to enhance the experience of the visitors.
There are no legal requirements for parents to leave any inheritance to siblings in any state in the United States. So unless the aunt were to challenge the will (which is impossible as she is deceased) there would be no need to find this person as they would have no legal claim to any assets .