My uncle has a will that states that when he passes he's estate goes to his wife and vise versa and in the event of both passing he's estate goes to he's son whom he has had nothing to do with for many many years and does not want he's son to get a single cent how can he make sure that he's son gets nothing?

He would need to either write a new will or a codicil to that effect. Is your aunt still alive? If she is, it is possible that, should your uncle predecease her, his son would inherit from her (assuming her will provides for the son too). In that case she might want to change her will too.