Step-by-step explanation:
In this question, Greta, a mother of 3 children and the widower of Mr Robert, devising all her estate to a womanizer Gary Watson; which, by will of Robert, is to be transferred to the Children equally after the death of Greta. So Yes, children have absolutely the legal rights in invalidating Greta's will on the basis of their father's will in which he clearly told Greta to transfer the property to his children. Now from the legal and Ethical point of view, a mother should not be allowed to disinherit her offspring. The only people entitled to receive parent's property should be their children. And also Greta has developed the problem of being forgetful, the case for the children would be super easy to win, plus the reputation of the womanizer would also help children in winning the case.