From James Enck (7.06):

Aoki means "Greentree" (literally it means blue tree, but the
Japanese are a bit vague with colours. In traffic, a green light to us is a
blue light to them).

Ooki means "Bigtree"

Ai as a first name can either mean love or indigo

Io as a first name I have never come across - could it be a strange
transliteration? The word "Ioo" with an extended "o" sound means sulfur.
And those are the only answers I know...