The fact that our Lord, Jesus the Christ used these books in His teaching is enough “proof” for me. Our Lord teaches about the resurrection, the only reference to the resurrection I’ve found in Scripture is in the Deuterocanonical books.
Ever read the Psalms or the book of Acts?
Here is one of many many examples:
Acts 2:25-32 wherein Peter cites Psalm 16:8-11
For David says concerning Him:
"I foresaw the LORD always before my face,
For He is at my right hand, that I may not be shaken.
26Therefore my heart rejoiced, and my tongue was glad;
Moreover my flesh also will rest in hope.
27For You will not leave my soul in Hades,
Nor will You allow Your Holy One to see corruption.
28You have made known to me the ways of life;
You will make me full of joy in Your presence.'4]
29"Men and brethren, let me speak freely to you of the patriarch David, that he is both dead and buried, and his tomb is with us to this day. 30Therefore, being a prophet, and knowing that God had sworn with an oath to him that of the fruit of his body, according to the flesh, He would raise up the Christ to sit on his throne,5] 31he, foreseeing this, spoke concerning the resurrection of the Christ, that His soul was not left in Hades, nor did His flesh see corruption. 32This Jesus God has raised up, of which we are all witnesses.
You also said:
His teaching on marriage, the two becoming one, the marriage being an everlasting, or at least life long, contract varies greatly from the OT book of Deuteronomy,
The only Scripture he cites is from Genesis - never the Deuterocanonicals.
but we find it clearly expressed in Tobit, along with several other examples of His teaching.
The Sermon on the mount
Cites only the Law, never the deuterocanonicals.
and the Lord’s prayer, from Sirach and Wisdom.
The Lord’s prayer cites nothing, nor is it found in Sirach or Wisdom.
Read these books with an open heart, you can’t help but find His Words.
Jesus taught from the Septuagint, which includes these books, The Church used these books for over 1500 years.
The earliest copies of the Septuagint we possess were produced not by Jews but by Christians. Hence the inclusion of the deuterocanonicals in them proves nothing. The Lord Jesus and the apostles in the New Testament never a single time cite the apocrypha and use the phrase “it is written.” They are not Scripture and are not binding upon any Christian person in any way whatsoever.