How do the 61927 actuators work in MK II crane set (42009)?
THe actuators both turn in the same direction, as there is a gearing “bridge” between the two axles driving the actuators that consists of 3 interlocking gears. 3 gears that interlock cause the 2 outermost gears to spin in the same direction. You can easily validate this with a small test setup using a Technic brick with holes, a small axl and a few gears and axle pins.

EDIT: For clarity, this picture shows how each of the key gears spin in this setup.



The two flat bevel gears marked with #1 spin in opposite directions from eachother, but this is possible because even though they are on the same axle (#2), they are not attached to this axle as the gears have a pinhole, not an axle hole, and hence they can spin freely (see part 87407 on Bricklink). It is likely gear #3 (marked in yellow) that is the gear that is driven, and its power and rotation is transfered to its twin gear which drives the other actuator (and spins in the same direction).