As I said above, I don’t mean to say that the Charming family lack intelligence. I just have the ( of course very subjective) impression that they have recently behaved a bit out of character.
I’m not sure it’s out of character so much as the Charming family have such good hearts that they don’t openly suspect people they’ve never met. Snow hears that Zelena knew Johanna and she instantly trusts her–I would say that’s actually in Snow’s nature, not outside of it. David was distrustful of Zelena but, like normal, Snow manages to talk him into it because David is better with a sword than his head (not a bad thing). Emma has about 1001 concerns right now, so a midwife looking after Snow is just a normal pregnancy thing and Emma’s distractions mean she doesn’t look closer.
Also, they villains have to be smart so that the story goes longer. If you have a dumb villain who plays their hand to early then there is no story. It has to look like Evil has the upper hand until Good inevitably wins.