This is probably too late to do you any good, but: I killed the sister who meets you outside (no, really Mephala, if you're trying to be subtle, telling me to kill the hostages and flat out telling me you're involved was not the way to do it). Turns out the blood of a twin was close enough to trigger the ritual anyway, a Spider Daedra appeared, I killed it, brought the wife back to the husband, and he got a dressing-down from her and angsted about getting people killed before giving me my reward.