1. It is not written in the Torah. Torah is Law e.g the commandments given somewhere in Book of Exodus and later complied in Book of Deuteronomy. Book of Genesis, Leviticus, Numbers, rest of Exodus and Deuteronomy are Jewish history.
Jewish history contradicts itself:
And He said, “Take now thy son, thine only son Isaac whom thou lovest,
and get thee into the land of Moriah, and offer him there for a burnt
offering upon one of the mountains which I will tell thee of.” (Genesis 22:2)
Later it says:
His sons Isaac and Ishmael buried him in the cave of Machpelah near Mamre, in the field of Ephron son of Zohar the Hittite, (Genesis 25:8)
So Jewish history needs to be taken with a grain of salt. Torah does not mention names, it is just commandments, not history.
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2. The story of the sacrificial son is that Abraham took a young child who had no idea what was going on and just tried to sacrifice him without any mutual understanding (Genesis 22). The account in the Quran is different, it talks about a young man as his son who discusses the dream with Hazrat Ibrahim (AS) and then tells his father to fulfill the command of God in which both submit to act of sacrifice. It is written that after Hazrat Ibrahim (AS) did the act of sacrifice, God then gave Hazrat Ibrahim (AS) the gift of Hazrat Ishaq (Qur’an 37:101-113). So Hazrat Ishaq (AS) can’t be the sacrificial son according to Qur’an since he was given as a gift later.
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3. The query is strange of yours regarding the prophets linage of Hazrat Ishaq (AS) since the covenant is that all children of Hazrat Ibrahim (AS) (Qur’an 2:124) would be included in favor, the sacrifice of Hazrat Ismail (AS) was that Hazrat Ishaq (AS) will go first in the favor while Hazrat Ismail (AS) will be ‘sacrificed’ to God, that’s why Hazrat Ismail (AS) was left behind to God (Genesis 21).
Hazrat Ismail (AS) was confirmed to be a prophet and Messenger of God (Qur’an 19:54), he and Hazrat Ibrahim (AS) also made a prayer that a Messenger among their children should be born (referring to the Last Prophet (PBUH) Qur’an 2:129), it seems that when children of Hazrat Ishaq (AS) lost their chosen status, God choose the children of Hazrat Ismail (AS) to continue the same mission (Qur’an 16:123).
In Islam, sacrificial son has no connection to covenant, it just means the one who got sacrificed was left in God’s care (Qur’an 14:37). Even if one thinks Hazrat Ishaq (AS) was the sacrificial son, it makes no real difference since both Hazrat Ismail (PBUH) and Hazrat Muhammad (PBUH) were chosen by God any way.
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You may also read ‘The Only Son Offered for Sacrifice: Isaac or Ismael’ by Abdul Sattar Ghauri for more details.