My dear trukin brother,
You are asking very good questions and it is good that you do. Please do not stop asking those questions. God uses our questions to get into His Word more. I am very sorry that there are professing Christians in the world who criticize those who are curious about the things in the Bible.
I am a conservative, evangelical pastor and you just keep "trukin" through the scriptures and your questions my brother.
I will always be happy to answer questions of any kind or sort without criticism. As long as they are not just meant to be argumentative and whimsical.
Keep TRUKIN for the Lord~!
PLEASE NOTE: Adam and Eve had "other sons and daughters" the Bible says in Gen 5:4
"After Seth was born, Adam lived 800 years and had other sons and daughters."
If a daughter started having children at any age between 15-25...well...you do the math. By the time Cain and Seth were only in the middle years...lets say 300 or 400 there were plenty of women who very distant relatives.
THAT...is the easiest answer I can give you without being complex. btw...this is the same answer I would give to argue why "...Cain went out from the Lord’s presence and lived in the land of Nod, east of Eden." Gen. 4:16. There were so many by that time.
Think about it. If just one daughter had a child every year or even every other year for 10, 20, 30 or even 100 years (after all...at that time that would still be very young) look how many people there would be. Multiply that by each daughter that had children, every grand-daughter maybe just 15-20 years later, etc, etc..etc...there would be towns of people...cities....just like Nod, where Cain dwelt.
Hope this helps~!