Thanks, Time. This has bothered me, too. I instantly thought of the Fritzl case in Austria when JC was discovered and automatically thought about the possibility of more pregnancies and what might have happened to them. I initially thought PG might have been trying to create his own harem, I'm not so sure now. But the absence of any boys and only 2 known pregnancies didn't sit right with me at first.
Now, though, I'm more of the opinion that we would probably know by now if there were more births as we do in the Austrian case. Unless, JC decided that she wanted this part of the horror kept private, as well. If so, I guess only time will tell, if at all. Also, it is possible they put JC on the pill and planned the 2 girls, Nancy could have got them for herself but gave them to JC, instead. Not safe, but not impossible.