Reading this article, the mother and father seemed to have intentionally omitted the trans child from the trust and will. Although the mother says to the adult son or daughter that they will share equally, this is not the fact on paper. The mother wants to maintain a relationship with both children, and is non confrontational. However, her feelings seemed to be in opposition to the paperwork.
One thing I just learned is that some legal documents don't travel well across state lines, and should be updated or rewritten by an attorney in the new state.