One pair of headlights operates from one battery (gnd to plus 12v), the other pair operates from the second battery (plus 12v to plus 24v). The pair that is operating from the "top" battery is running on 12 volts from 12v to 24v, not from ground, is the only twist to the picture. But the batteries see equal loads.
Now, if you have four batteries but only two are being used to run the headlights, as soon as you turn on the headlights you will create a charging imbalance between the two that see no headlight load and the two that are loaded. That is incorrect, for sure. You should probably tap both pairs of batteries for 12v use.