Defending three Okinawa-sized islands in a 1917 scenario

How would you defend three Okinawa-sized islands in 1917, with weak ports and no major support for at least two months?

Land six-inch guns, machine guns and mines quickly, disperse and protect them, and improve one port if mutual support between the islands makes that worthwhile.

The scenario requires holding three Okinawa-sized islands for at least two months without major support. The initial answer depends on the defender and location, so the question is recast as an isolated island group elsewhere in the world. Six-inch guns, machine guns and mines are proposed because the existing infrastructure limits what can be brought ashore. Dispersed positions protected with steel and concrete would make suppression and landing more difficult. The aim is to gain time and make capture costly, since inadequate ports prevent building a force able to defeat capital ships outright. If the islands are close enough to support each other, upgrading one port could permit heavier guns to be landed.