I don't think your over reacting. You're right, Marley didn't get the early learning Colt is getting so that's not fair to call her names like that. Plus, I too think they understand. I KNOW Curly does cuz even if I don't raise my voice, when I say "naughty girl" she puts her ears down and goes under the bed to sulk. So, if they understand "sit, stay, roll over, naughty, good, etc." why wouldn't they understand "stupid"?
Tell hubs to cool out and be nice!