Added to what Darrigs said,canonically Memetchi only has 1 sister who is Imotchi,Mumutchi is just a counterpart. (Darrigs,mind if you don't misinformate people with your fan stuff?)
Also logically,Obaketchis cannot have siblings as they are deceased Tamagotchis.
While on Kuromametchi's side,no siblings for him are made yet. (And i highly doubt it happens,because there are no sibling counterparts)
