Whoever wrote this is actually ignoring a few things. Immanuel is a Hebrew word (עִמָּנוּאֵל) which means "God is with us". Jesus is the English transliteration of Iēsous which is the Greek transliteration of the Hebrew Yeshua- YHVH our Deliverance. The author had to include Immanuel because it is part of the same sentence with "virgin".
However, the Hebrew word translated "virgin" is almah (הָעַלְמָה H5959), and it means "young woman". This word has nothing to do with being a virgin. If Isaiah wanted to say virgin, he would have said betulah (בְּתּוּלָה H1330).
This birth was to be a sign to Ahaz, who reigned 700 years before Messiah. It's impossible that Yeshua was to be the fulfilled sign to Ahaz because Ahaz was very dead when Yeshua was born.
"Therefore YHVH himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.
Butter and honey shall he eat, that he may know to refuse the evil, and choose the good.
For before the child shall know to refuse the evil, and choose the good, the land that thou abhorrest shall be forsaken of both her kings." Isaiah 7:14
This prophecy is fulfilled in the very next chapter:
"And I went unto the prophetess; and she conceived, and bare a son. Then said YHVH to me, Call his name Mahershalalhashbaz.
For before the child shall have knowledge to cry, My father, and my mother, the riches of Damascus and the spoil of Samaria shall be taken away before the king of Assyria." Isaiah 8:3
"And he shall pass through Judah; he shall overflow and go over, he shall reach even to the neck; and the stretching out of his wings shall fill the breadth of thy land, O Immanuel.
Associate yourselves, O ye people, and ye shall be broken in pieces; and give ear, all ye of far countries: gird yourselves, and ye shall be broken in pieces; gird yourselves, and ye shall be broken in pieces.
Take counsel together, and it shall come to nought; speak the word, and it shall not stand: for God is with us." Isaiah 8:8
So we can see that Immanuel and Mahershalalhashbaz are one and the same, and he is Isaiah's son- which was not born of a virgin. Isaiah confirms that his son was the fulfillment of this sign:
"Behold, I and the children whom YHVH hath given me are for signs and for wonders in Israel from YHVH of hosts, which dwelleth in mount Zion." Isaiah 8:18
If Isaiah 7:14 is a "dual-prophecy" or whatnot, then we have even bigger problems. First, Isaiah's wife would have to be a virgin when she conceived Mahershalalhashbaz, which wouldn't make the virgin birth that spectacular. But she wasn't a virgin because Isaiah specifically says he had sex with her.
Yeshua is not Immanuel. Isaiah 7 and Isaiah 8 have nothing to do with the Messiah. "They shall call his name Immanuel" refers to a nick-name God gave Mahershalalhashbaz, the son of Isaiah, whom Isaiah confirms is a sign to the people.