Check out this article on How to Contest a Will.
You had a loving relationship with your mother and she always said she would leave everything to you and your siblings, but after she died, you discover she had recently written a new will, leaving everything to her housekeeper. Is there anything you can do? If you believe a loved one's will is not valid, you may be able to contest it. But proving a will is invalid is difficult and this process should be undertaken only if you are sure there is something wrong.