Duolingo wants you to understand that that "kepī" specifically means "and [the] fathers," which is why the reverse order is deemed incorrect.
Once again, i put the subjects in a different order and the system told me i was wrong
why Muñi kepī issi ? If kepī is "the fathers" and kepi "fathers" ??
Lengthening the last vowel equals the meaning of the conjunction "and". I.e: They are mothers and fathers / They are the mothers and the fathers.
(There are no articles in HV)