I think the testificates breed like vanilla but I went and married one of the humans and had my own kids, after a dozen kids I finally had one grow up enough to marry them off to another human not in my family and I have my first grand kid!
It is my understanding that grand children are not a part of your bloodline and can marry into your bloodline, which is good because I only had two human villagers originalluy.
EDIT:
So I crafted some ice for when I was in the Nether to find that that doesn't help.
https://github.com/Funwayguy/EnviroMine/wiki/Temperature
According to this I need... cold water? Any idea how to get that?