Barring confirmation otherwise, it seems that Hamura was the first to awaken the Tenseigan. However, this presents a problem, or at least an oddity.
The Tenseigan seems to mirror the Rinnegan in several aspects. Both are more or less equal in power, both confer the use of Truth-Seeking Balls, and to awaken both, one must replicate the chakras of their initial wielders by merging that of their descendants. However, where the Rinnegan seems to be a diluted version of Kaguya's Rinne Sharingan, Hamura's Byakugan (and that of the Hyuga and Otsutsuki) seems to be identical to Kaguya's- in other words, she didn't have the Tenseigan. So the question is, why?
My personal theory is that Kaguya actually did have the Tenseigan, but generally kept it deactivated. Hamura thus possessed it as well, though he wouldn't awaken it until after her sealing. Meanwhile, when Black Zetsu later ressurected Kaguya, he used Madara's body as a base, which possessed Asura's, Indra's, and the Ten Tails' chakra, as well as a Rinne Sharingan. As a result, her newly-constructed body was able to use these traits as a base and rebuild her own traits off of them. So, her Rinne Sharingan was fully restored. However, Madara's body lacked any DNA or chakra of the Hyuga clan, and thus there was nothing to bolster her would-be Tenseigan. As such, only a default Byakugan was able to form in her new body.
What do you guys think?