In the event that the DNA analysis of the bone fragments is inconclusive, I would like to suggest that they be subjected to strontium and perhaps oxygen isotopic analysis. Archeologists have for some time used Strontium isotopic analyisis of human bones and teeth to determine whether human remains found at sites were local residents visitors from far away. Strontium isotopic analysis of the Niku bone fragments could similarly indicate whether they are from coral reef dwelling Pacific islanders or people from farther away.
The basic idea here is that 'you are what you eat', ie. the isotopic content of human or animal bones and teeth record the isotopic composition of the food they eat. There are measurable geographic variations in the strontium isotopic composition of the earth's landscape (ie. rocks, soils, water) and so therefore there are geographic variations in the isotopic composition of the bones and teeth of animals and plants. The strontium isotopic composition of people who have spent their entire lives living on coral atolls should be quite similar to the strontium isotopic composition of the sea, and would be measurably different than the strontium isotopic composition of the bones and teeth of North Americans (e.g. AE and FN).
Bones that have been exposed for decades to the elements on Niku might isotopically equilibrate with the local environment, so if the strontium isotopic content of the bone fragments matches is that of the local environment, we can’t conclusively rule out that the bones are not those of a non-atoll dweller, but on the other hand if the strontium isotopic composition of the bone fragments is measurably different from that of the local Niku enviroment, that would strongly indicate that they came from an individual who lived somewhere other than a reef environment, as of course AE and FN did. Strontium isotopic anaysis would not prove that the bone fragments came from AE or FN , but they would be those of an ‘exotic’ individual.
Anyone interested in learning more about applications of isotopic analyses to archeology can easily find more information via Google.