Any person interested as or through a personal representative, trustee, guardian or other fiduciary, creditor, devisee, legatee, heir, next of kin, or cestui que trust, in the administration of a trust, or of the estate of a decedent, an infant, mentally incapacitated person, or insolvent may have a declaration of rights or legal relations in respect thereto:
§ 527.040, RSMo