Will and transfer of property

Hi,

A father wants to do a registered will of his property in favour of his son.

He has 2 daughters and his wife as well who will have a share in his property in case he dies

As of today, both daughters and wife are in favour of the will but since the future is uncertain, the son wants to know what he could get in addition to the will so after the death of father, he can get the property transferred in his name without having to ask his sisters and mother

Please advise