When I have Karlov of the Ghost Council and Soul Warden on the battlefield and I cast something like Lingering Souls, does Karlov get two +1/+1 counters twice since two spirits enter the battlefield or only once since I cast Lingering Souls once?

The same thing applies to beautiful cards such as Conqueror's Pledge - does Karlov get two +1/+1 counters six times or only once?