Most likely the first name is a variant spelling of a Sanskrit origin name triveNI [dental unaspirated t- (like in French), -r- roughly as in English, short -i- as in English "hit", voiced unaspirated labiodental -v- (i.e., between English v and w), long -e- as in English "tale", retroflex -N- and long -I as in English "heat"): the tri- in that means and is cognate with English three, and the second part comes from the root ve meaning to weave and means a braid. It thus means triple braided, but since the junction of rivers was also described as the braiding of the currents, the common meaning is a confluence of three rivers, in particular the one where the North Indian rivers Ganga, Yamuna, and the mythical Saraswati join. This is a holy confluence for the Hindus, and the site of religious pilgrimage.
Pillay is a last name of Tamil and Malayalam speaking land-owning communities, often Hindu, but also belonging to other religions. I don't know Tamil, so can't comment on its meaning and it may be related to a word meaning child. But it was originally a title bestowed ceremoniously by South Indian rulers, and became a last name (or sometimes caste marker) in the communities mentioned above (and rarely in others). The particular spelling (as opposed to Pillai, Pilli, and a variety of other transliterations) is very common in South Africa, though it is also found in India and other communities of Indian origin.