Aunt's property encroached by cousin. She has no heir. What to do?

Our property has two plots one 63 another 63A. There ate two different propert deeds and taxes are also seperate for these two plot of lands. Now this 63A belongs to my aunt, she is a widow, senior citizen without any heir, one of my cousins has iilegally encroached one her propery by building a entension and joined the two properties and did his kitchen and bathroom over the encroached property. My question how this can be resolved and if she makes a will and gives her property to me, can it be challenged by other cousins after her death or gift deed is abetter idea???