I asked a divinity school professor how the inheritance rights of parents are. “Parents can give however they want, children cannot question it.”, he answered. Can parents give the inheritance more to ones and less to others when distributing?
According to the Quran, inheritance is not an issue left for us to decide. Allah the Almighty has determined all the criteria and the portions regarding the distribution of inheritance in the Surah an-Nisa, verses 11-12 (see: the Quran 4:11-12). He then states that those are the limits of Allah and condemns those who transgress His limits by disobeying His orders to eternal deprivation (see: the Quran 4:13-14).
However, it is a possibility that parents could have given some of their property to some of their children as a gift during lifetime, causing an injustice to other children. One narration from the Prophet Muhammad on this issue goes like this:
“Amir ash-Shabi said: I heard An-Nu’man bin Bashir on the pulpit saying, ‘My father gave me a gift but ‘Amra bint Rawaha (my mother) said that she would not agree to it unless he calls Allah’s Messenger to witness it. So, my father went to Allah’s Messenger and said, ‘I have given a gift to my son, but ‘Amra bint Rawaha ordered me to make you as a witness to it’ Allah’s Messenger asked, ‘Have you given (the like of it) to every one of your sons?’ He replied in the negative. Allah’s Messenger said, ‘Be afraid of Allah and be just to your children.’ My father then returned and took back his gift.’ ” (Bukhari, Gifts, 11.)
According to this narration, we have to say that parents should not discriminate on their children while giving them some property during their lifetime, as it will cause an injustice toward the others.