Legal Question in Wills and Trusts in California

If relevant they should be admissible if properly introduced. "Malice and hostility" do not necessarily prove there is a conflict. You would benefit from consulting with an attorney.

He can hate your guts and still properly fulfill his fiduciary duties to you. Trustees must be removed for objective misconduct, not subjective feelings. Unless you can show he is actually doing something wrong as trustee, a court will have no interest in hostility in text messages. About the only point at which such messages would be relevant is if you had already had him removed for actual misconduct, sued him for any financial damages you can prove you suffered, and are trying to get punitive damages.