Who Else Besides Adam and Family?

In Genesis 4 10 - 16, it is stated,

10 The LORD said, "What have you done? Listen! Your brother's blood cries out to me from the ground. 11 Now you are under a curse and driven from the ground, which opened its mouth to receive your brother's blood from your hand. 12 When you work the ground, it will no longer yield its crops for you. You will be a restless wanderer on the earth."
13 Cain said to the LORD, "My punishment is more than I can bear. 14 Today you are driving me from the land, and I will be hidden from your presence; I will be a restless wanderer on the earth, and whoever finds me will kill me."
15 But the LORD said to him, "Not so [e] ; if anyone kills Cain, he will suffer vengeance seven times over." Then the LORD put a mark on Cain so that no one who found him would kill him. 16 So Cain went out from the LORD's presence and lived in the land of Nod, [f] east of Eden.

In verse 13, Cain said whoever finds him will kill him. So far, we only read about Adam, Eve, Cain and Abel. Abel was dead, so who are the other people besides them? Surely Adam and Eve wont kill their own son.

Then in the next verse,

17 Cain lay with his wife, and she became pregnant and gave birth to Enoch. Cain was then building a city, and he named it after his son Enoch. 18 To Enoch was born Irad, and Irad was the father of Mehujael, and Mehujael was the father of Methushael, and Methushael was the father of Lamech.

Cain got married and started his family. But who was his wife? It should be someone from outside Eden, as Adam and Eve did not give birth to any others so far.

Then in verse 25,
25 Adam lay with his wife again, and she gave birth to a son and named him Seth, [i] saying, "God has granted me another child in place of Abel, since Cain killed him." 26 Seth also had a son, and he named him Enosh. At that time men began to call on [j] the name of the LORD.

So it is quite clear here that while Cain were living his own life with another group of people, Adam and Eve gave birth to Seth. Eve said Seth was in place of Abel, implying that from the time Abel died till now, she did not give birth to any son. Or maybe did not get pregnant at all, further supporting that there were other people besides the Adam family.

Genesis 5 contains the genealogy of Adam, and the line is definitely different from that of Cain. Even Abel and Cain are not mentioned. Hence, we can safely conclude that Cain married outside the family of Adam and started his own line. Thus, it shows that Adam and Eve were not the only living people then.

In Genesis 6, we are told that the sons of god married the earthlings. Who are these beings? Very likely they were aliens who came to earth and married the earthlings. the Bible-god was their leader.