Has anyone had success contesting a will due to undue influence? How hard is this to prove and how costly would this be? We have three avenues (mental capacity/undue influence and family provision) any help will be appreciated!
These circumstances play out surprisingly often, and unfortunately pursuing legal remedies tends to end up being rather costly. Therefore a depending on the value of the estate, much of it can be consumed by legal fees. For this reason, most cases do end up settling. It is difficult to say whether it is 'easy' to establish these types of cases. Generally I would say that undue influence, or lack of capacity are not especially hard to prove if you have the right evidence. Family provision applications are generally easier to make out. But between the three causes of action you have outlined above, you may have fairly good prospects of recovering an inheritance from the estate.
Generally, a Will must be made at the absolute discretion of the testator and be free from factors that taint the testator's capacity. However, courts also place great emphasis on the testator's words/intention and presume that there is no issue of capacity unless this can be proved by the objecting party.
Contesting on the basis of undue influence is quite difficult since the courts have held that there must be "coercion" shown. Undue influence is more than just mere persuasion or influence or pressure due to feelings of sympathy/guilt/gratefulness. The courts have recognised that family members often have some sort of influence over will makers (testators). If the testator was elderly, then you could look at getting statements from hospital staff, any comments made by family members that may cast doubt on the testator's capacity, medical reports and statements by medical professionals are a general starting point.