"My mother sees the father."

Translation: Ñuha muña kepe urnes.

[kaligoth]

Ñuha muña kepe urnes = Is father not "kepa"?

[xPsGoDWh]

In the nominative, yes. In this case, it's an object, not a subject, and needs to be in the accusative. In that case, the ending changes from -a to -e, at least for this class of nouns.