One reason I wanted to reprint your letter is to encourage every reader to do everything they possibly can to avoid situations like this. God is not honored when conflicts like this break out, and unfortunately, resentment and jealousy (and greed) can poison a family for years to come.
Even if we have very little, it's still better to make our wishes known through a legal will than to leave a legacy of conflict and bitterness behind. In Old Testament times, a number of laws dealt with inheritance, partly to avoid controversy. Jesus had nothing in the way of possessions, but before His death He made sure that His mother, Mary, would be taken care of (see John 19:25-27). The Bible says, "A good person leaves an inheritance for their children's children" (Proverbs 13:22).
What can you do? First, don't add to the problem by demanding things that others clearly want. Yes, you may lose something that has sentimental value to you, but it's better to do that than to lose a friendship. Perhaps your example will encourage others to do the same.
Then pray for your extended family. Right now, they aren't at their best and they need to realize it and not let things take the place of Christ. Above all, never forget (and urge others in your family never to forget) that when we know Christ, we have "an inheritance that can never perish, spoil or fade.... kept in heaven for you" (1 Peter 1:4).