The scientific evidence does not support the possibility of a world wide flood. Therefore it was a local flood.
The “sons of god” are not angels, they are God’s chosen people. Angels are messengers and servants, not the children of God. Thus Genesis chapter 6 is about who Cain and Seth married, which is not sisters never mentioned in the text but the daughters of all those other people out there who Cain was so afraid of in Genesis 4:14. The children were giants among men, i.e. men of reknown – leaders of human civilization, not some weird half human hybrid (which makes for great fun in sci-fi films, I admit, but not reasonable for the religion of rational people).