These books were in the Jewish Septuagint which Jesus and the Disciples referred to, they were read by Christians throughout the centuries and were included in the first editions of Luther's Bible and the KJV (King James Version) and in all Bibles until the late 1700s to 1800s.
They are inspired just as the Song of Songs etc. were
In fact 2 Maccabees 7 is what Hebrews 11:35 refers to
Some links between this book and the NT: Matt. 24:15 15When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:) -- this is tied to 2 Macc. 8:17 [17] Setting before their eyes the injury they had unjustly done the holy place, and also the injury they had done to the city, which had been shamefully abused, besides their destroying the ordinances of the fathers.
While in Luke 24:4 and Acts 1:10 - Luke's description of the two men in dazzling apparel reminds us of 2 Macc. 3:26
The links also extend between this book and Revelation
Rev. 17:14 14These shall make war with the Lamb, and the Lamb shall overcome them: for he is Lord of lords, and King of kings: and they that are with him are called, and chosen, and faithful. - description of God as King of kings follows 2 Macc. 13:4 But the King of kings stirred up the mind of Antiochus against the sinner, and upon Lysias suggesting that he was the cause of all the evils, he commanded (as the custom is with them) that he should be apprehended and put to death in the same place.
you can find out more at this link
The Roman Catholic, Oriental Orthodox and Eastern Orthodox include the deuterocanonical books. The basis for these books is found in the early Koine Greek Septuagint translation of the Jewish scriptures. This translation was widely used by the Early Christians and is the one most often quoted (300 of 350 quotations including many of Jesus' own words) in the New Testament when it quotes the Old Testament.From the same link above,According to J. N. D. Kelly, "It should be observed that the Old Testament thus admitted as authoritative in the Church… always included, though with varying degrees of recognition, the so-called Apocrypha or deuterocanonical books."
The traditional explanation of the development of the Old Testament canon describes two sets of Old Testament books, the protocanonical and the deuterocanonical books. According to this theory, certain Church fathers accepted the inclusion of the deuterocanonical books based on their inclusion in the Septuagint (most notably Augustine), while others disputed their status based on their exclusion from the Hebrew Bible (most notably Jerome). Michael Barber argues that this time-honored reconstruction is grossly inaccurate and that "the case against the apocrypha is overstated"
Besides moving the Apocrypha to a lower level, Luther also did many other canon-related things. He argued unsuccessfully for the relocation of Esther from the Canon to the Apocrypha, since without the deuterocanonical sections, it never mentions God.And Esther is in all OTs, right?