"The father loves the mother."
Translation:Kepa muñe jorrāelza.
Kepa is the subject of the sentence, therefore it is in the nominative case. And since the father is only one person, it is jorrāelza (he/she/it loves) instead of jorrāelzi (they love). Muñe is the accusative singular and states "who" the father loves - which is the mother. It is the object of the sentence.