(◕◡◕)So I spoiled the chapter for myself yet again.
I translated the last page of 106. Kate says she is Kate Mirror and came to get back the shadow house/ mirror house (thanks google translate). And damn! I am hyped! Although I would need to wait some more for the next chapter.
She really is connected to the true owner of the house. And apparently is the rightful owner now.
G. Grandfather is probably that son who stole his sibling's inheritance or even some guy not born into the lineage who used his shadow's abillity to make himself a noble displacing and/or killing the noble family (Kate's family). Or he could have married into the house and his greed coupled with the shadow ability made him take over and Kate (most probably her parents) had to run away to survive. Now Kate is back for what is rightfully hers.
Another thing could be that the Shadow (Mirror) family could have originally been owned by noble humans who were peacefully united with morphs/shadows or viceversa or even a union between shadow and human (hence Kate is born a shadow that doesn't need to imitate a human as morphs do) without the whole prisoners of the house, kidnapping children and so on thing but the g. grandfather changed it and now Kate as rightful heir wants to restore the house to what is was and not the prison it is now.
All in all, looks like that headcanon of sweet grandpa and the 4 crazy aunts and uncles will only live in my crack fanfic of the shadow house being a good place, a home to many children with Grandpa, uncle and aunts, annoying big brother Edward who thinks he is all that but really just pisses everyone off... He was never sweet because Kate clearly dislikes him. Anyway, I always love a dysfunctional family au.
I am hyped!
The hype is real. I can't wait for more. So many theories and questions running through my head!