When I have [mtg:Karlov of the Ghost Council] and [mtg:Soul Warden] on the battlefield and I cast something like [mtg:Lingering Souls], does Karlov get twice the +2/+2 counters since two spirits enter the battlefield or only once since I cast Lingering Souls once?

The same thing applies to beautiful cards such as [mtg:Conqueror's Pledge] - does Karlov get 6 times +2/+2 or only one?