That arrangement might turn out to be typical, but it isn't necessarily guaranteed. There's a standard set of Joker parents, but there are alternative parents, too, and the possibility of no parents at all, for instance. I'd need to see more Elspeths to tell whether there are more ways to get them than with a Bell/Edward pairing, and I'd need to see more Edwards before I could tell you if there are alternative sources for those than Libbies and Edward's biological father's template. (If he even is a template. Some people just aren't, contagion or no.)