Lack of future planning (SPOILERS)

Noah told everyone almost as soon as he found out about Ila's pregnancy that he would kill any girls. His family had 9 months to come up with some kind of plan to prevent that and they apparently gave no thought to it until it was go-time. They could have protected those girls. There's no way Noah could have gotten through three healthy young men, especially being his own sons; a healthy adult woman, especially being his wife; and finally, a weak, but determined young woman, especially one he considered his daughter, in order to get to the babies. I doubt he could have both physically and psychologically even made it through his sons.

I know, for storytelling purposes, he had to make the decision himself. But the family sounded determined to keep the potential girl(s) safe and yet they only had a hastily thrown-together plan that, of course, barely delayed Noah.

FURTHERMORE, what was Noah's plan after this? Ila is now fertile. Was Noah going to stalk her for the rest of his life, as he gets older and older, slaughtering any girls who dare to exit her womb?

This was the most interesting part of the movie to me, but it didn't make any sense.

Please don't feed the trolls.