If a person is of sound mind, but has been inveigled into willing property, does that constitute grounds to contest will?

Is the person alive or dead? If they are alive, have them make a new will. If they are deceased, the will is either valid or its not. There are grounds for filing a will contest (called a caveat). In a caveat, the whole will is invalidated if grounds are established. Fraud or fraudulent inducement would be among the grounds but you do not give enough information/details as to what exactly occurred to know if any will caveat would be successful. Litigation is a costly and time-consuming affair and should not be entered into lightly. For a caveat to be successful, you will have to have a good case and be able to substantially benefit if the will is invalidated. Would you stand to inherit? What is the value of the probate assets and what would your share be if you prevailed? Would it be worthwhile to pursue litigation from a cost-benefit analysis? For example, it would make no sense to spend $10,000 on litigating a caveat if you are only going to recover $5,000. It would make sense if you are going to recover substantially more. I suggest that you make a copy of any estate file (if there is one) and discuss this case with a probate litigation attorney to see if it makes sense to bring a caveat. In the alternative, you might be able to bring some kind of action against the beneficiary of the beneficiary who received the real property under the will and seek to impose a constructive trust on it. For example, say an older widowed man met a young nightclub dancer who was a gold digger and who prevailed on him to give her expensive gifts and leave her a substantial inheritance in his will. The man then dies and his children could bring a lawsuit against the gold digger alleging that she used fraud/undue influence to get the man to give her lavish gifts or a lavish inheritance.