Well, the same thing happened to me. One, are they too hungry? Two, this sounds really dumb but put two guys set to breeding prefrence and go take a shower. Mine will not breed while I'm looking. Make sure to keep the view away from the hut. I don't know why but mine only worked that way. They don't like you looking or something. And the population will go up before they enter the hut so you can breed them 100 times a minute if you have to. They don't HAVE to go into the hut, they just do.