Property and will

My father left a will and where he wished all his property in the name of our mother during her life time and after her death, his granddaughters and grandsons (one Major and others minors) will inherit the property. However, he mentioned that if granddaughters and grandsons do not serve my mother then, she can remove any of granddaughters and grandsons by way of will to any other person We are three brothers and one sister, but our father did not mentioned our name, due to which our mother thinks father was wrong. So can she amend or do something about it. Moreover, can his grand daughters and grand sons (one Major and others minors) do “Haq Tyag” (forgo) as some are willing to do this What will be treatment of minor ..can he do “Haq Tyag”.