icdbd-QA/0010: Ruling on discriminating among children

My husband has 2 siblings, an elder brother and sister. My parents in-law are very biased about their daughter. So much that my father in-law already declared that his property will be divided into 3 equal shares. I, on the other hand, am the only child of my father, and as per Islamic rule I will get only half of his properties, which I am okay with. But still I consoled my husband saying that it is his father's property and he can decide what to do with it. This is just one example, there are so so many of them. My husband is their youngest child and is very emotional. He is in huge mental unrest! So, I want to know whether there is any such ruling that prevents parents from doing such discrimination.