You gotta water ohia everyday in Waianae or it will die. Ohia has to have water, main thing.

Hilo ohia are used to being very wet. It's easier to just buy one that's been doing well on Oahu. Kind of hard to lug a potted plant on the plane. I don't think you can take soil between islands. But anyway, your brother's plants are free right?

Maybe you can get seeds from a plant already growing on Oahu. Shake the seed capsule over a pot of moist potting soil. Transplant keiki when they have 2 sets of leaves. Ohia grows pretty slowly. It could take a year to get a 2-foot plant from seed.

You can use 2 parts potting mix to 1 part cinder to grow ohia in a container.

Use a slow release fertilizer like Osmocote, the one that has all the numbers the same (like 14-14-14, for example)

I recommend Heidi Bornhorst's book, "Growing Native Hawaiian Plants." Good luck!