It can be difficult to get both parents to sign a form when they live in the same household and therefore it is helpful that I can allow one parent to sign. However in the case of a divorced family, I want a parent in each household to sign in order to be certain that both parties have a say in permissions, etc.
Requiring signatures from 2 households on one form is particularly troublesome when the second person who signs is the one who submits the form, and they have the option to change the first signer's entries.