Doug Mason : I do not know which source was used for the NWT OT.
In Appendix A3 of the Study Edition of the New World Translation it identifies the sources used for the NWT OT:
Hebrew Text: The New World Translation of the Hebrew Scriptures (1953-1960) was based on Biblia Hebraica, by Rudolf Kittel. Since that time, updated editions of the Hebrew text, namely, Biblia Hebraica Stuttgartensia and Biblia Hebraica Quinta, have included recent research based on the Dead Sea Scrolls and other ancient manuscripts. These scholarly works reproduce the Leningrad Codex in the main text along with footnotes that contain comparative wording from other sources, including the Samaritan Pentateuch, the Dead Sea Scrolls, the Greek Septuagint, the Aramaic Targums, the Latin Vulgate, and the Syriac Peshitta. Both Biblia Hebraica Stuttgartensia and Biblia Hebraica Quinta were consulted when preparing the present revision of the New World Translation.
Doug Mason: ...note that "The Kingdom Interlinear Translation of the Greek Scriptures" states that its Greek text comes from Westcott and Hort.
In the Foreword of The Kingdom Interlinear Translation of the Greek Scriptures, pp.8,9 it says :
The Greek text that we have used as the basis of our New World Translation is the widely accepted Westcott and Hort text (1881), by reason of its admitted excellence.* But we have also taken into consideration other texts, including that prepared by D. Eberhard Nestle,** the Spanish Jesuit scholar Jose Maria Bover,*** and another Jesuit scholar, A. Merk.**** The UBS text of 1975 and the Nestle-Aland text of 1979 were consulted to update the critical apparatus of this edition.
Footnote *: Besides using the 1948 Macmillan Company edition of this text, we have availed ourselves of the two exhaustive volumes on Matthew and Mark, prepared under the supervision of S. C. E. Legg, A.M., and published by the Oxford Clarendon Press, Novum Testamentum Graece Secundum Textum Westcotto-Hortianum - Evangelium Secundum Matthaeum (1940) and Evangelium Secundum Marcum (1935).
Footnote **: The 18th edition of Novum Testamentum Graece by D. Eberhard Nestle, elaborated by D. Erwin Nestle, published in 1948 by the Wurttemberg Bible Socicty, Stuttgart, Germany.
Footnote ***: Novi Testamenti Biblia Graeca et Latina by Joseph M. Bover, SJ, dated 1943 and published at Barcelona, Spain.
Footnote ****: The 1948 printing of the sixth edition of Novum Testamentum Graece et Latine by Augustinus Merk, S.J., and printed at Rome, Italy.
Doug Mason: They might have come from the original languages ...but...the veracity of those sources, requires the expertise of scholars in Lower (Textual) Criticism, such as Emanuel Tov.
Westcott, Hort and Lightfoot were the leading textual critics of their day. Before criticising them have a read through Hort's Introduction and Appendix to get a flavour of their expertise.
Their work was of such a high standard that 100 years later Bruce Metzger was reported in Bible Interpreters of the 20th Century, as saying (p.264):
“The international committee that produced the United Bible Societies Greek New Testament, not only adopted the Westcott and Hort edition as its basic text, but followed their methodology in giving attention to both external and internal consideration”