I don't know the significance of repetition in the Aboriginal languages concerned - my completely uninformed guess would be a plural.

Not as such, in any one I've come across. (As opposed to e.g. Malay-Indonesian, anak-anak = 'children'.) Aboriginal languages typically don't have plurality in nouns. Reduplication has some morphological function, clearly, but in odd ways, e.g. names of colours in Bidyara if I remember rightly.

Pago Pago is Samoan, so the <g> is nasal [N] as in <singer>. Samoan forms plurals of some nouns, but with a variety of means: reduplicated syllable, vowel lengthening.

If the two <a>s are different, perhaps one is long: as in <pucker> vs <parker>, but I don't know.