Russell had the idea of a 1,000 year long trial of resurrected people apparently as a way to reconcile various conflicting Christian doctrines/interpretations with each other, including the doctrine of Universalism and of a restitution of all. At least that is the impression I got from reading portions of the his Studies in the Scriptures volumes. He also had the idea that 'the day of the Lord/Jehovah' was much longer than one solar day. Also a Bible verse says that a 1,000 years to the Lord/Jehovah is as just one day, and compare that to the account of Adam being told that if he ate the forbidden fruit he would die in that very day to the verse which said Adam lived for 930 years.
As to where Martha, if she existed, got the idea of resurrection on the last day, she got it from some of the Jewish groups (such as the Pharisees and Essenes) which were in existence before the year 1 CE/AD. They were teaching the resurrection and their ancestral community likely got it from the Persians (while the Jews were in Persia/Iran). The Persian/Iranian worshipers of the god/lord Ahura Mazda believed in the last days, a judgement day, in a resurrection, and in a future battle between the forces of good (and light) and evil (and darkness).
Pagan religious ideas can not be completely removed from Christianity (without a tremendous change to Bible based Christianity), since pagan religious ideas are a substantial part the both the New Testament and the Old Testament sections of the so called 'Holy' Bible. Similarly, some pagan Greek philosophy is included in some of the wisdom teachings attributed to Jesus in the Bible (and even Paul quotes pagan Greek philosophers authoritatively). And, some pagan Egyptian religious philosophy has been adapted into some of the wisdom teachings of the book of Proverbs. For example of the latter see Proverbs 22:17 - 23:35 in the Bible and see the translator's note for 22:19 in the Catholic Bible called the New American Bible (NAB) - not to be confused with the protestant New American Standard Bible. In that Catholic Bible (at least in the OT translation copyright 1970) the phrase "words of Amen-em-Ope" is used in verse 19!
Regarding the words of the scribe Amen-em-Ope see also page 315 of a massive book published by Abingdon Press called The Interpreter's One-Volume Commentary On The Bible: Introduction and Commentary of Each Book of the Bible Including the Apocrypha, With General Articles, Edited by Charles M. Laymon; copyright 1971. The Editor's Preface of that book says the following.
"The authorship of this volume is varied in that scholars were chosen from many groups to contribute to the task. In this sense it is an ecumenical writing, Protestants from numerous denominations, Jews, and also Roman Catholics are represented in the book. Truth cannot be categorized according to its ecclesiastical sources. It is above and beyond such distinction." The main scripture text used for this commentary is the Revised Standard Version of the Bible. Page 315 of the commentary, under the heading of 'III. The "Thirty Sayings" (22:17 - 24:22)' says in part the following.
'This collection is in some way directly dependent on the Egyptian Instruction of Amen-em-Opet. The translation of an obscure Hebrew phrase as thirty sayings in 22:20 (KJV "excellent things") is based on the fact that Amen-em-Opet's book contains 30 chs. In 22:17 - 23:11 every proverb but one (22:26-27; most of these proverbs consist of 2 vss. each) has a more or less close parallel in the Egyptian book, though the order is different. The quotations below from this work are from the trans. by J. A. Wilson in J. B. Pritchard, ed., Ancient Near Eastern Texts, pp. 421-25." '
By the way, in support of the accuracy (and prophecies) of the Bible, the WT a number of times has quoted from editions of the book called Ancient Near Eastern Texts. For one example of such, see source reference number 6 to a quote in chapter 9 of the WT book called THE BIBLE--God's Word or Man's? For two other examples see source reference numbers 23 and 25 of the WT book called Is the Bible really the Word of God?