So Kankri is the descendant of Karkat, right? Well, I told this to my friend and we had a little discussion, so I was wondering if you can provide a bit more of an explanation for that, and also answer her question. She wanted to know "But if Karkat and Signless existed in the same timeline, then who's the Signless?"

Karkat created two groups of trolls, his group and Meenah’s group. His team was created first then their genetic material was mixed up to create Meenah’s team. Pre-scratch it was Karkat and his group who grew up to be the ancestors and Meenah’s group were the kids playing sgrub. They did a scratch and their roles were switched; post-scratch it was Meenah’s group who grew up to be the ancestors and Karkat’s group who were the kids playing sgrub. The Signless is post-scratch Kankri.