I don´t know how these things are legislated in England, but I can explain how it works here.
I have two sisters. One of my sisters sadly passed away a few years ago. Our mother is still alive, but when she passes away, my living sister and I receive 1/3 each, the last 1/3 will be divided between my deceased sister´s children. Not through a will, this is the law here. I think it might very well be the same in England.