These manga focus on pairs of twins, whether it's solely the twins, or it includes twins as part of a relationship, ie a love triangle, as well as stories about parents raising twins. Twincest included too.
This is a complete list of every manga and light novel published in English by Dark Horse Comics. These are either incomplete, ongoing or fully published in English.
List of completed and ongoing manga and light novels that are licensed in English (it can cover US and UK).
All mangas in this list are published in Poland.
Somewhere about "The Innocent" the order is not random anymore.