Look at the picture. Say who Bill (Mag) is for... Example: Bill is a son for his mother. Mag is a daughter for her mother. ...for his / her grandmother. ...for his / her father. ... for his / her sister. ...for his / her grandfather.

Bill is a grandson for his grandmother/grandfather 
Bill is a son for his father
Bill is a brother for his sister
У Мэг всё наоборот: для отца она daughter, для бабушки/дедушки то же самое но с приставкой grand. Для сестры она, я думаю, сестра.