This particular problem is attributed to Alcuin. The wording does not give sufficient information to answer the question without making legal assumptions. Please share your assumptions with your solution.

A dying man left 960 shillings and a pregnant wife. He directed that if a boy was born, he should receive three-quarters of the whole and the child's mother should receive one-quarter. But if a daughter was born, she would receive seven-twelfths, and her mother five-twelfths. It happened however that twins were born - a boy and a girl. How much should the mother receive, how much the son, and how much the daughter?