It isn't just for renters. I made that clear. I said the problem for OWNERS and landlord. OWNERS meaning house/property owners. By, tenants, I meant the person occupying the dwelling. No, you cannot just toss a person out immediately. Depending on the states laws:
Possession is nine tenths of the law. The brother is in possession of his room, and thus the house. He has lived there long enough and has his possessions in there, and has established it as his residence. PERIOD.
All the other details I added were just that. Details. He is in possession of the room. He has established residence. The courts will ultimately
agree that he is a squatter and a trespasser and then continue with the eviction proceedings, but will take time to get him out. Courts usually give a reasonable amount of time, after legal notification, to find a new, appropriate home. This is why it may not be an immediate process.
There have been episodes on this on Dr. Phil., where parents where trying to evict deadbeat, older children who did not have ANY legal claim to the house EXCEPT that they live there, their possessions were there and it was considered by the law and the police, that that is his residence until a court order says it's not. Some had even broken back into the bedroom and moved all their stuff back in, when the parents were away.

UNTIL the parents had a court order stating the person no longer has
any right to live there, the police's hands were tied.
Do you know how many people would just be calling up the police
every day, when they've had a disagreement with someone they are living with, who is not on the deed or lease, and wanting the police to toss the other person out on their ear saying they were trespassing?

EVERY person not on a deed or lease (which is most people: spouses, children, relatives,) could then be tossed out
any day, on the whim of the owners. On the 18th birthday, the police could be called in to toss out ANY child. The laws do not work that way.
The police do not operate that way, when they can plainly see THE PERSON LIVES THERE. They need a court order stating the person no longer has legal claim to be there, before they or a Sheriff can come in and toss the person and their possessions out on the street. The police do not
interpret the laws, they enforce then. that's why in a domestic situation, they need LEGAL PROOF that the brother no longer is ALLOWED to live there. One cannot just show the deed, if his possessions are there, and he might even have a driver's license or other documents proving he it is his established residence.
You are confusing a person's established
possession of a residence/home, with being a trespasser or squatter. The law understands that people live SOMEWHERE, (unless they are truly homeless. Even then, they can establish the cardboard hut they've made into a home. People live SOMEWHERE.) Certain laws protect that right. On the deed, Yes, he may be a trespasser or squatter, but in a state where "
Possession is nine tenths of the law," he has a right to be there over the current paperwork, until the courts change his status with a Sheriff's Order of Eviction.
The OP needs to find out her laws in her state as to what she needs to do as executor as well as owner. They may be different. She will most likely have to send notification, by certified mail, to the brother that he must vacate by the legally allowed time, and give him the legally required time to do so. Otherwise, he can claim he was never told to vacate. Only then, may she be allowed to advance with eviction proceedings, if he has shown he will not move.