Question:
If in the beginning there was only Adam and Eve, then they had their children, where did their children’s wives come from?  If it was only Adam and Eve, does this mean that biologically we are all related?

Answer:

While the Bible is silent on this, we can only believe that as Adam and Eve had more children, they would marry each other and have children.  While this may sound terrible to us today, it was not until the giving of the Law that one was forbidden to marry a close relative (read Leviticus 18:6-18).  Yes, we are all biologically related.