If the Alternian trolls are Post-scratch and the Beforan trolls are pre-, and the Beta kids are Pre- and the alpha kids are post-, then (ecto?)Biologically Kankri is Karkats son, Meenah is Feferis daughter, etc. just a thought.

Technically speaking, yes, The Beforan trolls are the offspring of the Alternian trolls’ pre-scratch counterparts. 

~Mod T