Most pacific islands are coral atolls on top of extinct volcanos/seamounts. All of which will eventually sink (even Hawaii !)
The idea they're sinking because sea levels are rising in response to global warming is entirely unproven. The same was once claimed of the
Maldives, until long term studies revealed the opposite.
Swedish scientist Professor Nils-Axel Mörner presented
this
paper to the UK Parliament in March 2005 which concludes:

...observational data do not support the sea level rise scenario. On the contrary, they seriously contradict it.

See also
this article from the Telegraph written in 2000