They say only male cockatiels can talk but I had a female who used to say hello. I think females talking in some species are just less likely rather than impossible. As for the parrotlets I see no reason why they can't learn the odd word. Just don't expect it to be clear.
I agree with marie on that one. I've spoken with two amazon breeders and one amazon fanatic (he had like 17 birds lol) and they all agreed that female amazons actually ended up speaking more.