I'm not a lawyer and couldn't give you a legal angle, however I can tell you from personal experience that when my father passed away a few years ago, my brother raised a dispute with regards to property - after many months of lawyers hashing it out, the end result was that my father's last written wishes were honored.

My condolences to your family and I hope everything gets resolved - it has been my experience that death, wills and money can bring out the worst in people.