I don't know for sure why they're doing that, either. Cats are such mysterious creatures.
My cat, Elvis, was not a big talker when I adopted him. Now that he has been here for several months, he has started meowing a lot more often, among other positive changes in his behavior. I like to think that it's because he's happy here. One of the cute things he does is, if I'm in another room, he meows until I call out to him, "what's the matter, baby?", then he comes running to me.
Maybe your kitties approve of their new home and are just trying to tell you so.