السلام عليكم
Bani Ishaq probably means the Edomites, because Prophet Isaac had two sons according to the Torah: 1. Esau and 2. Jacob. The Israelites are progeny of Jacob, while the Edomites are progeny of Esau. According to Judaic tradition, the Romans were identified with the Edomites, and by extension Edom came to represent Christendom.
Bani Ishaq is therefore, most likely, a reference to Mediterranean peoples, like Italians, Greeks, Anatolians, Syrians.
A Hadith states that 70,000 of Bani Ishaq will attack and conquer Constantinople but without weapons. They will instead say لا اله الا الله والله اكبر and one side of the city will fall to them, and say it again and the other side will fall (this is referring to the two parts of the city, one that is on the continent of Europe and the other that is on the continent of Asia). Then they will say it a third time and the "gates" of the city will be opened to them.
Now immediately after this "spiritual" conquest, it will be announced that the Antichrist has emerged and so they will drop everything and go back.
This gives us a clue that these 70,000 will probably be on the eastern side of the Mediterranean, on the continent of Asia, so probably a group of Syrian or Anatolian Muslims, since the fitna of the Antichrist is from the east, not from Europe.
Now there is another Hadith regarding the final conquest of Constantinople right before the emergence of the Antichrist, coincidentally also reported in the Sahih Muslim as the previous Hadith, but the problem is this one appears to contradict the former because it describes a conquest through force of arms:
It says that the Romans will land at Dabiq or A'maq, but those who will go to fight them are not described as "Bani Ishaq" but rather people of Medina. Now the reason for the Roman invasion is because apparently a group of Muslims have captured some prisoners from among the Romans, and the Romans are demanding that the Muslims coming out of Medina to face them should not interfere in the Romans going after specifically that group which captured prisoners. But the Muslims of Medina will refuse to stand aside and will fight the Romans. As a consequence of this war, Constantinople will be conquered. The Hadith mentions that the Muslim conquerors will be hanging their swords on the olive trees when a devil will announce that the Antichrist has emerged among their families. Now when they turn back and reach Syria then the Antichrist will have actually emerged.