The Greek word for "brothers" here is adelphoi (Strongs G80). This means literally "brothers". However, it can also mean "countryman" or "followers". The NET Bible (which uses the most current translation, taking advantage of the latest in linguistic scholarship) translates this as "brothers and sisters". The footnote for this says of this word:
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2 Consider it pure joy, my brothers and sisters, # 1:2 The Greek word for brothers and sisters (adelphoi) refers here to believers, both men and women, as part of God's family; also in verses 16 and 19; and in 2:1, 5, 14; 3:10, 12; 4:11; 5:7, 9, 10, 12, 19. whenever you face trials of many kinds, 3 because you know that the testing of your faith produces perseverance.
The same store carried other Bible translations that used gender neutral renderings. These other versions were simply less well-known. The Council on Biblical Manhood and Womanhood is very involved in these issues from a conservative point of view, and are opposed by the Christians for Biblical Equality .
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In the Bible, the Greek words adelphos and adelphe were not restricted to their literal meaning of a "full brother" or "sister," and nor were their plurals.  From an early date, there were varied discussions to interpret whether the Greek term adelphos —applied in these circumstances to people described as adelphoi (brothers) of Jesus ...
Another instance of the use of common gender noun is the Greek "adelphos" or "adelphoi." Previously this word has been translated into English as "brother," "brethren," or "brotherhood." But the Greek (and its Hebrew equivalent) can mean either physical or spiritual relative/s or "brothers and sisters" and often referred to the whole Church.
The NRSV regularly translates adelphoi as "brothers and sisters", and the most recent edition of the Good News Bible does likewise. I appeal to you therefore, brothers and sisters , by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship.
It would seem that the scribal change (Variant 1/WH) was trying to bring the second-person plural, "you know that" in agreement with the plural address (ἀδελφοί μου adelphoi mou) "my brothers and sisters," in the previous verse, James 5:19.
The point is, in the New Testament the Greek word adelphoi is being used in the Hebrew sense of kinsman/ kinswoman, or Covenant brother or sister. We know from the Bible and other sources that Jesus had several kinsmen who became prominent in the Jerusalem New Covenant Church.
A Review of the 2015 Amplified Bible in Paperback, from Zondervan. April 18, 2016. April 18, 2016. Bob Snyder. Instead of going through and listing several changes between the older Amplified Bible and the new for 2015 Updated Amplified Bible, I decided just to show one as a brief example. Then I will explain some pros and cons.
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