The first Christians were Jews and were accustomed to Jewish scriptures which became Christian scripture as well.
Ancient Greek translation of the Jewish scriptures. This was an Old Testament source for early Christians.
There are no Jewish Christians.
The majority of people who refer to themselves as "Jewish Christians" have zero Jewish heritage, they are mainly Christians.
Leviticus.
Yes, the Jewish Bible is composed entirely of Hebrew scriptures, with the exception of a few passages in Aramaic.
The Tanach (Jewish Bible) is written in Hebrew.
genesis
The first Christians were Jewish.
yes
Christians believe that Jesus was the Jewish Messiah. Jews disagree.
Catholics, and Christians in general, refer to the Hebrew Bible as the Old Testament. A more refined answer would note that Catholics accept the Apocrypha as canonical while Jews do not, so the Hebrew scriptures accepted by Catholics include the Jewish Hebrew Bible plus the Apocrypha.
The Talmud