Hi Natalie 85
Two females cannot make babies ..it has to be a male and a female. I find switching the villagers that you are using to "Parenting" often does the trick. Sometimes they can't make more babies because they need more huts (the game will usually tell you this). Sometimes they are too hungry to be fertile.
To make potions the alchemy lab has to be fully repaired, (That's just to the left of the science lab, under the same roof). A master scientist will repair the alchemy lab if she/he is dragged to all the three jugs, one bowl, and the stick .... which you have to find.
Why the potion-making villagers should disappear, I don't know, they usually tell me that the lab needs repairing.