Is the questioner obligated, according to Islamic law, to carry out his father's will to care for his paternal aunt, especially since she receives a sum from social security, and her grandchildren are well-off and some of them refused to care for her, given the advanced age of the questioner and his wife? And would he be sinful if he brought her a maid from her own money without her consent?

The paternal aunt is a relative with whom ties of kinship must be maintained, and this has been confirmed by your father's will. Therefore, you should continue to treat her kindly and assist her. Her grandchildren are also obligated to do so, especially if she is in need of money, due to the obligation of a well-off descendant to support a needy ascendant. It is not permissible to bring her a maid from her own money without her consent, but try to convince her of this and apologize to her for any shortcomings. Advise her grandchildren concerning her and remind them of her rights over them.