One of the recommendations thread prompted me to remember this story about a group of children (pairs of twins) that were placed there by aliens to see how they would grow and develop. The twins are paired sexually (so I suppose its incest). The first event is the death of the first twin that was placed too early by herself. This leaves the second twin to mourn her death and becomes embittered without his twin mate (who later kidnaps someone's daughter to take as his mate). The main character is another twin pair, who later discovers some ESP like powers in some rock. He becomes a leader of sort but has to abandon his peers because gets into conflict with another twin pair. And so the story goes with him developing technologies in this untamed wild planet.
I think the first book is monogamous with his twin mate but turns into harem in the second book? I think that's where I stopped reading. For the life of me I can't remember the title nor any of the names. Anyone remembers this?