That's often the point of riding two abreast. If you are riding one at a time and on the edge of the lane then cars will often try and overtake you without leaving the lane, or at least a minimal amount. That leads to very dangerous close passes.
If you ride side by side or in the middle of the lane if alone, then generally the times you get passed by cars are much safer as if going fully into the other lane already they tend to give you enough space.
This would depend on the drivers in your area, but with the shitty Sydney drivers I learnt quickly to hold the lane unless it was a safe place for them to pass.
Also, because traffic is a thing it's very rare that I don't end up right behind whatever car passed me at the next traffic light, safer passes don't really cost much time for the driver once traffic is accounted for
They're little sea puppies that are perfectly happy to cruise around while you swim with them. At least that's the grey nurse sharks we get in aus. The ones you're describing sound more like wobbegongs or similar. The grey nurses need to be in highly oxygenated water.
Grey nurses also used to have a rep as "man eaters" but that was just because of how they looked,not any actual attacks