wills

As-Salam `Alaykum! My question is regarding estate distribution. Our family has got a land which my grandfather had bought long before. My father has died 11 years back i.e. before my grandfather. My grandfather also passed away some 7 years back without distributing the land among his children. He has 4 sons including my father and 4 daughters. Now our eldest uncle says that grandson has no share in grandfather's estate and as my father is also not alive he will also not get the share. So I just want to ask whether ISLAM has such a condition that a son after death does not have share in fathers estate and even the grandson instead of his father cannot have a share? If so, I will forget about it because following Allah’s teachings takes priority over any other consideration. I hope you will understand my question and guide me on the right path. Thank You

I wanted to ask about the permissibility of writing a will in the case where it may go against the rules in the quran. The situation i have in mind is that my Sister and her husband who have a one year old son, would like to write in their will that if anything were to happen to both of them then they want myself and my husband to look after him.  This is because they feel that we would be best able to take care of their son and bring him up in an islamic way etc.  We would be happy to do so in such a situation. Is this permissible?