No, the PCs can't see through the darkness
The spell darkvision simply gives the PC darkvision just as if it were naturally granted by some other feature.
You touch a willing creature to grant it the ability to see in the dark. For the duration, that creature has darkvision out to a range of 60 feet.
And the darkness spell specifically says that a ...
Yes, the creatures are affected if the player aimed at the right spot regardless (e.g. if he knew exactly where they were because he heard them)
The Player heard them, aimed where he thought they were, so unless some Meta is involved which the DM could had handled differently, knowing their location is not required; luck could have been on his side too.