Can 15 years of stay give the person any legal right over the property

After my father's death, my aged mother continued living in the same old property owned by three of us (legal heirs) - me, my elder brother and mom. In last fifteen years we have allowed a person of my trust to live in the same property with his wife so that they can look after my mother as me and my brother are relocated in different cities. Can this 15 years of stay give the person of trust any legal right to this property? If there is slightest possibility, what kind of legal precaution we can take to safeguard our ownership as we don't want to ask the person to leave at the same time.