Right now, and for a limited time remaining (to hear some agents tell it), it is legal to build two, quite large houses on a lot in HPP. One may drive down the dead end of 19th Ave., Hilo of Kaloli, and witness, on the Mauka side, one lot with two very large, new, quite legal, two-story homes. Don't tell anyone, but they are ideally designed to divide into two units each. Shhhhh. There are several identical arrangements here and there in the park.
There are also a number of two dwellings on one TMK arrangements in Hawaiian Beaches/Shores/Parks/Shores Rec Estates as well. Many of those are quite legal, permitted, and taxed.
Houses in Puna with ohanas do seem to be uncommon. In fact, it seems to be about the inverse of Maui, where, in the working-class areas, the house without at least one extra "unit" wedged in there is as rare as an albino monk seal. Creative folks manage to cobble together 3 or 4 units on 6,500-10,000 SF lots in Kihei. Lots of rule-bending going on there. Parking is at a premium on those lots and the adjoining streets. There are not many open, sunny spots to grow food. That's for sure. People need places to live, though.
There are also a number of two dwellings on one TMK arrangements in Hawaiian Beaches/Shores/Parks/Shores Rec Estates as well. Many of those are quite legal, permitted, and taxed.
Houses in Puna with ohanas do seem to be uncommon. In fact, it seems to be about the inverse of Maui, where, in the working-class areas, the house without at least one extra "unit" wedged in there is as rare as an albino monk seal. Creative folks manage to cobble together 3 or 4 units on 6,500-10,000 SF lots in Kihei. Lots of rule-bending going on there. Parking is at a premium on those lots and the adjoining streets. There are not many open, sunny spots to grow food. That's for sure. People need places to live, though.
I wish you all the best.