26 C.F.R. § 20.2056A-9
Section 2056A(b)(2)(C) provides special rules where more than one QDOT is established with respect to a decedent. The designation of a person responsible for filing a return under section 2056A(b)(2)(C)(i) (the Designated Filer) must be made on the decedent's federal estate tax return, or on the first Form 706-QDT that is due and is filed by its prescribed date, including extensions. The Designated Filer must be a U.S. Trustee. If the U.S. Trustee is an individual, that individual must have a tax home (as defined in section 911(d)(3)) in the United States. At least sixty days before the due date for filing the tax returns for all of the QDOTs, the U.S. Trustee(s) of each of the QDOTs must provide to the Designated Filer all of the necessary information relating to distributions from their respective QDOTs. The section 2056A estate tax due from each QDOT is allocated on a pro rata basis (based on the ratio of the amount of each respective distribution constituting a taxable event to the amount of all such distributions), unless a different allocation is required under the terms of the governing instrument or under local law. Unless the decedent has provided for a successor Designated Filer, if the Designated Filer ceases to qualify as a U.S. Trustee, or otherwise becomes unable to serve as the Designated Filer, the remaining trustees of each QDOT must select a qualifying successor Designated Filer (who is also a U.S. Trustee) prior to the due date for the filing of Form 706-QDT (including extensions). The selection is to be indicated on the Form 706-QDT. Failure to select a successor Designated Filer will result in the application of section 2056A(b)(2)(C).
26 C.F.R. §20.2056A-9