Challenging a will isn't easy; in the vast majority of cases, decedent and his or her attorneys will have appropriately drafted and executed the will. However, if the right circumstances exist, it's certainly is possible to successfully challenge a will on legal grounds.
Here the most common complaints by which someone can seek to challenge a will:
Lack of testamentary capacity
When a will creator has testamentary capacity, it means that he or she is legally permitted to create and execute a will. In most cases, this means that the individual was at least 18 years of age when he or she created and signed the will and was of sound mind to understand what the document entails.
Undue influence, forgery and fraud
Another common complaint against a will is that the document is a fraud. A fraudulent document may be created under undue influence -- if the testator was manipulated into signing the will because he or she did not have the free will to decide whether to sign it. A will could also be challenged on the grounds that it was fabricated, the signatures were forged, or other types of fraud were committed during the creation of the document.
Another will is the "true" will
Another common technique is to bring forth another will -- either an older one or a newer one -- and prove that this will is more important should be used instead of the other one.
There are more ways to challenge a will than these. Therefore, potential heirs and those who stand to benefit if a will is invalidated may want to investigate this matter further to determine whether sufficient legal grounds exist to challenge the will in their cases.