How much is the Septuagint Apocrypha considered part of Scripture?
The book of 2nd Maccabees was written by Jewish rabbis in the greek language in the community of Ellenic Jews in Egypt. It contains perspectives of the Jewish rabbis and became part of the Greek septuagint read mainly by Ellenic/Greek Jews in the Roman empire. It was written after the Maccabean revolts, I think in the 2nd century BC after the Old Testament proper had already been written.
The Hebrew Tanakh is the Old Testament. TANAKH (T.N.K) stands for TORAH (the first five books of the Old Testament), Nevim (the prophetic books like Isaiah and Jeremiah), and Ketuvim (the writings, as in the book of Daniel and the Psalms). The Greek Septuagint Apocrypha like 2nd Maccabees is not part of the Hebrew Tanakh. Paul wrote his letters in the middle of the 1st century AD. In 90 AD, the Judaic Rabbis decided to exclude 2nd Maccabees and the Apocrypha from the Old Testament. Early Christian saints debated among themselves whether the apocrypha was canonical. I think that for a long time in the west they were called deuterocanonical, or semi-canonical.
In the middle ages, the Catholic Church decided that some books like 2 Maccabees were fully canonical, while the protestants disagreed among themselves about whether to even include the apocrypha in their printings of the Bible.
2 Maccabees 7 - the Prefigurement of Christ
Judaism claims that no such thing as a person acting as an atonement is possible in Scripture.
2 Maccabees 7 relates a story when seven brothers were killed by a pagan king because they refused to eat pork. The pagan king gave the youngest brother a choice to eat the pork or die. The youngest brother's mother told him to refuse in order to follow God's rules. The youngest brother told the king that they were sinners, but hoped that their deaths would persuade God to have mercy on His people and sooner stop His punishment of them.
So here we have the concept of an atoning sacrifice in scripture, despite what modern Judaism proposes to the contrary.
Of course, 2 Maccabees claims to be more of a historical narration, which records the brothers' words. It doesn't literally say that God accepted the brothers' request. After all, Moses made a request to be an atoning sacrifice for His people, but God denied Moses' request. So we don't know whether God accepted the brothers' request.
On one hand, the youngest brother explicitly said that they were suffering for their own sins. Yet the lambs and Christ were sinless, so the brothers might not have matched the requirement for a perfect sinless sacrifice. On the other hand, I think that the Maccabean revolt against the pagans was eventually successful and a Judean government was restored, wasn't it?
Either way, 2 Maccabees 7 at least presents the concept of an atoning sacrifice, a prefigurement of Christ.
The martyrs of 2 Maccabees 7 are martyrs in the Orthodox Church. It seems that St Paul refers to the mother's sons' martyrdom in Hebrews 11:35 when he talks about the persecution of Old Testament saints in Hebrews 11:32-40,
Hebrews 11:35: women received their own dead ones as resurrected, others were tortured, not accepting freedom, in order to receive a better resurrection.