He is what is known as a tenant at sufferance. A tenant at sufferance is someone who has no right to occupy the premises, but is tolerated by the owner and may be terminated at the will of the owner.
A tenant at sufferance has few rights, but one of these rights is to be evicted. So in other words, one cannot simply physically kick him out of the home. He must be evicted like a tenant who has not paid rent. If after the quick eviction hearing she still does not leave, then, one can get a Writ and have the authorities forcibly relocate him.
However, many tenants at sufferance simply LEAVE once they are given notice that they will be evicted if they do not, since they have really no defense to an eviction.
So here, you may:
1) Give him notice to leave and if he does not;
2) Evict him as though you would a tenant; and
3) Have the authorities remove him by force if she still does not leave; and
4) Change the locks.
Again, the majority of tenants at sufferance shall leave upon notice, or shortly after an eviction is filed.
The notice should be at least 15 days.
It doe not matter that he is related. At 18, he becomes an adult and parental care ends.
NOTE that if he is threatening you or hurting you, then a quicker way is available possibly. Let me know if you want information on this.
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