Jesus close relatives called “adelphos” were not all first cousins so the word "anepsios" would not fit for them all.
The New Testament writers used the Septuagint , a Greek Translation of OT. , when quoting the Old Testament 300 times out of the 350 total quotes of OT.
The New Testament writes followed the pattern of the Septuagint where “adelphos” is used for all close relatives, first cousins and other relatives as well.
“adelphos” is a compound Greek word literally meaning “from the same womb”
However we can prove the Bible does not use that restricted meaning.
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G. and B. your questions will have to wait till later,