when can you not have someone change their will

There is not a hard rule about when someone can or cannot change a Will: the question is whether the person who is making the Will has the required level of mental capacity to make a new Will, and a related question is whether the person really wants to make the change or whether someone else is effectively forcing him to make the change through the exercise of undue influence. The fact that someone is suffering from a severe illness and undergoing potentially debilitating treatments does not necessarily mean that either the person does not have the capacity to make a Will or that they are under someone else's undue influence, although those are certainly factors to consider in making those determinations. The standard for capacity to make a Will is fairly low, and it only has to exist at the actual time the Will is signed. The person basically has to know who he is, who the members of his family are, what he owns, what the Will says, and that he intends to sign it as his Will. The standard for determining whether one person is being unduly influenced by another person is fairly high, on the other hand. Basically, there has to be a close enough relationship and a fairly high degree of control exercised by the influencer over the other person. If a child believes that the father didn't have the required degree of capacity at the time the new Will was written, or that the new Will was the product of undue influence, then the child can try to contest the Will if it is offered for probate. That is estate litigation and should generally not be attempted without the help of a good fiduciary litigator. In order to preserve the right to contest the Will, the child should not sign any paperwork presented without first reading it very carefully and ensuring that the child isn't consenting to having the Will admitted to probate. The child should also be prepared to act very quickly; the time limits for Will contests in Georgia are pretty short.