2 questions about Christian Religion &/or The Bible?

To answer # 1 - when Adam & Eve were alive, their bloodline was pure, so God allowed them to mate with one anothers' sisters/brothers/etc; since the Flood, the bloodlines have been mixed, so therefore the practice of what is called is forbidden. For # 2, you will get many ideas/theories on this subject; it's best to look at some of the Bible commentaries available (www.twft.com is one source) for further information