So the eldest sister and younger brother are both intelligent but the middle child is a fool.
Perhaps the reason the parents left behind the property to the middle child is because they knew that she is a dumbass unlike her other siblings who will make it far in life.
So, Gu Ming and Gu Si are geniuses and Gi Yin is an idiot... "Like Ma'am, you've been uncovered"!!! And I bet the parants knew it so gave the properties so Gu Yin đ§đ¤