Angelos, which Quranic verse mentions Issac and Jacob as brothers??
Well, the writers of the Quran did not know until late that Ishmael was Abraham’s son. This is why they repetitively referred to Jacob as Abraham’s second son!

Pay attention to the verses below:
EARLY PERIOD OF THE QURAN: ABRAHAM’S TWO SONS WERE ISAAC AND JACOB NO ISHMAEL!!!
6: 84 We gave him
Ishaq and Ya’qub: all (three) We guided: and before him, We guided Nuh, and among his progeny, Dawud, Sulaiman, Ayyub, Yusuf, Musa and Harun: thus do We reward those who do good.
11: 71 And his wife was standing (there), and she laughed: but We gave her glad tidings of
Ishaq, and after him, of
Ya’qub.
12: 6 “Thus will thy Lord choose thee and teach thee the interpretation of stories (and events) and perfect His favour to thee and to the posterity of Ya’qub, even as He perfected it to thy fathers **Ibrahim and Ishaq **aforetime! for thy Lord is full of knowledge and wisdom.”
12: 38 "And I follow the ways of my fathers,
Ibrahim, Ishaq, and Ya’qub; and never could we attribute any partners whatever to Allah: that (comes) of the grace of Allah to us and to mankind: yet most men are not grateful
19: 49 When he had turned away from them and from those whom they worshipped besides Allah, We bestowed on him
Ishaq and Ya’qub, and each one of them We made a prophet.
21: 72 And We bestowed on him
Ishaq and, as an additional gift,
Ya’qub, and We made righteous men of every one (of them).
29: 27 And we gave (Ibrahim)
Ishaq and Ya’qub, and ordained among his progeny Prophethood and Revelation, and We granted him his reward in this life; and he was in the Hereafter (of the company) of the Righteous.
38: 45 And commemorate Our Servants
Ibrahim, Ishaq, and Ya’qub, possessors of Power and Vision.
However, Muhammed’s scribes added Ishmael’s name to Abraham’s progeny first in a late Mecca period - by omitting Jacob - , but they were not courageous enough to ascribe Kaa’ba’s construction to Abraham yet!
14: 39 "Praise be to Allah. Who hath granted unto me in old age
Isma’il and Ishaq: for truly my Lord is He, the Hearer of Prayer!
(Muhammed’s scribes were probably praying: "Praise be to Allah. Who has granted unto us in old age the information that Ishmael was Abraham’s first son

)
In Medina period, nevertheless, Muhammed’s scribes always added Ishmael to Abraham’s progeny although sometimes it caused bigger mistakes:
MEDINA PERIOD: ABRAHAM’S SONS ARE ISHMAEL AND ISAAC. (ISHMAEL IS ISAAC’S FATHER!)
2: 133 Were ye witnesses when Death appeared before
Ya’qub? Behold he said to his sons: “What will ye worship after me?” They said: “We shall worship thy God and the God of thy fathers, - of
Ibrahim, Isma’il and Ishaq, - the One (True) God: to Him we bow (in Islam).”
2: 136 Say ye: “We believe in Allah, and the revelation given to us, and to
Ibrahim, Isma’il, Ishaq, Ya’qub, and the Tribes, and that given to Musa and 'Isa, and that given to (all) Prophets from their Lord: we make no difference between one and another of them: and we bow to Allah (in Islam).”
**2: 140 **Or do ye say that
Ibrahim, Isma’il, Ishaq, Ya’qub, and the Tribes were Jews or Christians? Say: Do ye know better than Allah? Ah! who is more unjust than those who conceal the testimony they have from Allah? But Allah is not unmindful of what ye do!
3: 84 Say: “We believe in Allah, and in what has been revealed to us and what was revealed to
Ibrahim, Isma’il, Ishaq, Ya’qub, and the Tribes, and in (the Books) given to Musa, 'Isa, and the Prophets, from their Lord: we make no distinction between one and another among them, and to Allah do we bow our will (in Islam).”
4: 163 We have sent thee inspiration, as We sent it to Nuh and the Messengers after him: We sent inspiration to
Ibrahim, Isma’il, Ishaq, Ya’qub, and the Tribes, to 'Isa, Ayyub, Yunus, Harun, and Sulaiman, and to Dawud We gave the Psalms.
Gabriel’s apology: Forgive me Muhammed rasulullah, it was my fault to confuse Isaac with Ishmael and Ishmael with Jacob. Too much noise up here! So please do not send your army upon me and do not stop interceding for me on the day of Judgment.
Peace,
Angelos N.