You really shouldn't be concerned about this rating thing. In EU PEGI rated Demon's Souls, Dark Souls I, II, III and Bloodborne the same rating of 16.
ESRB rated Demon's Souls, Dark Souls I and Bloodborne M while Dark Souls II and III are rated T, though if you read the descriptions it doesn't make much sense since the contents are really similar.
If you watch the Dark Souls III gameplay you'll see they're using some blood effects from Bloodborne and the game's still T rated so I wouldn't pay much attention to this, it's a Souls game like the others.