Hello,
I agree with ivory as material of the hilts and would put both in the 19th century. But maybe here are better experts for this knives. Of course I can only speculate if they have a similar age but they are looking so (same style and same signs of age).
I have such a knife, too, but with a black coral handle and more "accessoires". Maybe the blades of your Piha Kaettas had a similar inlay in the fullers like my knife has but it was lost:
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