It is always difficult to prove undue influence regardless of the state. You have to ask yourself what evidence you have of the undue influence. Was the most recent will drafted and handled by an attorney? Did the nephew draft it and put it in front of him? Was anyone else present? Was there a mental exam near the time of the signing? You should hire an attorney or have a consultation to explore your options but be forewarned it can be a difficult road and one that involves out of pocket legal fees if you lose.
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/