The Bible clearly shows us the only people on the ark were Noah, his wife, Noah’s three sons, and their wives.
Genesis 6:17-18: “And, behold, I, even I, do bring a flood of waters upon the earth, to destroy all flesh, wherein is the breath of life, from under heaven; and every thing that is in the earth shall die. But with thee will I establish my covenant; and thou shalt come into the ark, thou, and thy sons, and thy wife, and thy sons’ wives with thee.”
Genesis 7:7: “And Noah went in, and his sons, and his wife, and his sons’ wives with him, into the ark, because of the waters of the flood.”
Genesis 7:13: “In the selfsame day entered Noah, and Shem, and Ham, and Japheth, the sons of Noah, and Noah’s wife, and the three wives of his sons with them, into the ark;”
Genesis 7:23: “And every living substance was destroyed which was upon the face of the ground, both man, and cattle, and the creeping things, and the fowl of the heaven; and they were destroyed from the earth: and Noah only remained alive, and they that were with him in the ark.”
I Peter 3:20: “Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.”
The Bible tells us all mankind came from Noah’s three sons.
Genesis 9:19: “These are the three sons of Noah: and of them was the whole earth overspread.”
The Bible tells us Noah was perfect in his generations.
Genesis 6:9: “These are the generations of Noah: Noah was a just man and perfect in his generations, and Noah walked with God.”
Noah was perfect in his generations. The Bible does not say this about Noah’s wife, his sons, or his sons’ wives.
The only way Cain’s descendants could have survived the flood is through those who were on the ark with Noah.