If Gods children commited inbreed, does this mean he approves brothers & sisters to have with eachother ?

After my last question about how Adam & Eve were able to reproduce mankind, a lot ( a lot ) of people said :'they had more children, than Cain & Abel' . So inbreed must have been the case. Does this mean he approves in present time relatives having with eachother and getting married ? Or is it a sin ? Give me good arguments !!