I have a suggestion: if clanmates being able to kill/hurt each other gets added, the parent or mentor of the cat who killed/hurt another clanmate will react either disappointed, sad, or angry.
I actually think that happens to an extent, I've had things happen where its like "Weedclaw gets into a fight with clanmate over leadership." and sometimes when you look at the cats description after they've healed it'll say "Weedclaw was left scarred after a fight with a clanmate." I've had bloodthirsty cats scar and kill cats in their own clan it's just rare. the only thing that isn't in the game is others reactions to this