when is a will disputable?  

Hi there :) To the best of my understanding, a will remains entirely valid unless there is a codicil or a whole new will drawn up to replace it. That's why it's important to have your will changed or updated any time there are major changes such as births, deaths, marriages, divorces, etc. Anything that affects your civil status should also be reflected in the will, if it means that you'd want things to be distributed differently.