Would 'newest' make sense? If not, how would one translate 'the newest member?'
Could this also be "the very young member"? That translation is currently marked as incorrect, general strengthening on web.
I would argue that 'νεότατος' is used only for 'youngest' in fact, not for 'newest'.
Would καινουργιότατος/καινουργιότερος be the best superlative to use for 'newest'?
Ο νεότερος or ο πιο καινούργιος/νέος. Don't forget the definite article but remember there is still ambiguity since these terms are not distinct from the comparative. Ι would expect to hear "καινουργιότατος" only when joking: "Αυτό δεν είναι απλά καινούργιο, είναι καινουργιότατο!" Καινουργιότερος sounds made up. ;)