They didnt cut him because of his mental state, they cut him because they have penetrative haki like oden.
[automerge]1596857429[/automerge]
Having penetrative haki ignores durability therefore kaidos skin turns into normal skin, wb was getting stabbed by fodder.
So yes they can stab him but if you like the AP it dont mean much you know, so yes she stabbed him but the damage was that of someone of her lvl and it seemed to amount a needle prick on him, and the combined attack of them using that penetrative haki made him bleed out of the mouth. This is good for kaido too because it shows that even if you ignore his durability his str/endurance is still extremely high.
@HA001 @LANJI CUCKSMOKE , does that sound like a good explanation to you all?