"E hīmeni kūlauna kākou!"

Translation: Let's harmonize!

[Riceburns]

"Letʻs all sing in harmony!" is another acceptable translation.

[RonRGB]

(link) https://manomano.io/definition/26430

kūlauna

[MK] 1 vs

In harmony, in music. Kūlauna ka hīmeni ʻana o lākou. Their singing is in harmony. E hoʻolohe kākou i nā leo kūlauna. Let’s listen to the harmonizing parts. Comb. kū + launa. See hoʻokūlauna. Hīmeni kūlauna like. To sing in harmony.