angels most certainly bred with human females.
this was not heavenly fathers fault, for he created free will for all. so don't go saying he is evil for letting it happen. do you think he's evil now for things similar to this happening today? of course not. we do what we want to do. it's not his fault that some choose evil.
did he step in immediatley when adam and eve sinned? no. he let them complete thier sin and then went to talk to them about it, after they made plant clothes for themselves.
heavenly father allows you to hang yourself. he watches and records your actions. if he interceeded, you would not do what you were going to do. that's the test. what are you going to do, right or wrong?
the angels came down and did what they did, and then heavenly father pronounced judgement on them. they damned themselves. he watched and judged. the innocent humans caught in the situation were helpless. when adam and eve ate from the tree they chose thier new evil master. they decided who they would listen to. and their new evil master did not care at all about them.
it wasn't until christ's time that we got to switch sides and get some protection.