I been doing some research and i think your grandfather is a brother of one of my great grandfathers. Their parents were Faigata Tiumalu and Taitai Samataua. A lot of da info came from familyresearch.org, so it still needs verification from originals, but the dates seem to match up.
This is for sure per court document Tiumalu v Faiivae: Falo had two brothers Viavia Tiumalu and Faamao Tiumalu and an adopted sister Faanenefu. Their dad passed away so their uncle Salesa took them as his own. Hope this helps!!