Kia ora Mais, You have a couple of great answers here! I recently joined italki as a Te Reo Māori teacher so if you are looking for support or partnership with learning the Māori language I would love to help!

ngā karu is eyes õna karu is his/her eyes õku karu is my eyes

Mais you may have already figured it out but there are only a few words in Māori that change when plural. Like tamaiti/tamariki tangata/tāngata. Mostly plurals are demonstrated by the determiner He karu - an eye/ some eyes Ngā karu - the eyes Te karu - the eye