music, melody
喈 centers on harmonious sound: music and melody. The given meanings are closely linked as expressions of ordered, pleasant sound.
喈 combines 口 (mouth) with 皆, which likely contributes the sound and the idea of togetherness, suggesting voices or sounds coming together in harmony.
A mouth 口 making sound together with everyone 皆 creates music and melody.
For カイ, imagine a choir singing in harmony: the sound 'kai' echoes as they all open their mouths together. Kai -> カイ.