You neglected to comment on Isaiah 7:14 and it's placement in Matthew. Let's look at Isaiah 7 and 8 and you tell me why I would be wrong to assume that it's fulfillment is entirely within the context of Isaiah's text....
Isa 7:14 Therefore the Lord himself will give you a sign. Behold, the virgin shall conceive and bear a son, and shall call his name Immanuel.
Isa 7:15 He shall eat curds and honey when he knows how to refuse the evil and choose the good.
Isa 7:16 For before the boy knows how to refuse the evil and choose the good, the land whose two kings you dread will be deserted.
Isa 7:17 The LORD will bring upon you and upon your people and upon your father's house such days as have not come since the day that Ephraim departed from Judah--the king of Assyria."
First, Ahaz is being told that YHWH will give HIM a sign... The sign is for AHAZ... agree? Which two kings did Ahaz dread in Jesus' day 700 years later? Here's the fulfillment EXACTLY as told..... Isa 8:3 And I went to the prophetess, and she conceived and bore a son. Then the LORD said to me, "Call his name Maher-shalal-hash-baz; Isa 8:4 for before the boy knows how to cry 'My father' or 'My mother,' the wealth of Damascus and the spoil of Samaria will be carried away before the king of Assyria." The true Christian response from most theologians is that it's a "dual prophecy". It's the only explanation they can offer to try and explain away the simple fact that Isaiah had a son in the next chapter fitting the Assyrian king's demise as told in chapter 7!! Now, concerning the authorship of the gospels.... Who is Luke? As far as we know, only the letters attributed to Paul mention him. Luke isn't one of the 12 disciples, so exactly who is he? Now... just to show you that Paul and the gospels are definitely separate works and Jesus in the NT definitely said that he REJECTS PAUL.... 2Ti 1:15 You are aware that all who are in Asia turned away from me, among whom are Phygelus and Hermogenes. Here in his letter to Timothy, Paul mentions that "ALL who are in Asia (Ephesus is in Asia) turned away from me" Rev 2:1 "To the angel of the church in Ephesus write: 'The words of him who holds the seven stars in his right hand, who walks among the seven golden lampstands. Rev 2:2 "'I know your works, your toil and your patient endurance, and how you cannot bear with those who are evil, but have tested those who call themselves apostles and are not, and found them to be false. Jesus congratulates the Ephesian Asian church for rejecting Paul.... How do we know this? Because there are only 12 apostles of the lamb according to John, John by the way NEVER mentions Paul in any of his texts.... Rev 21:14 And the wall of the city had twelve foundations, and on them twelve names of the twelve apostles of the Lamb. There are only 12 apostles of the lamb... Paul is not one of them.