From a biological perspective the Augments were a `family` merely because they grew up together (and because Soong wanted them to feel like they had one for whatever reasons).
Genetically speaking, the Augments did not have a same set of parents.
Besides, incest is a culturally made up term and looked at mostly with distaste because it was labeled as such by society.
You have real life examples in which siblings have felt both sexual and emotional attraction towards one another ... or towards their parents ... and vice versa in numerous combinations.
Apart from it being 'distasteful' from societies perspective, it's hardly unnatural.
It may not be what usually happens, but it happens.
In the case of Augments, apart from being of the same race, to my knowledge they didn't have a same set of parents.
And to address the issue of the Augments not knowing to sew.
They probably had to learn on their own through improvisation as they were growing up.
Plus we don't know what circumstances they faced before we saw them on screen (which might explain their garments).
They were after all genetically enhanced humans, and were able to adapt to various environments ... so the garments were not a top priority for survival.