DC-DC converter double pins
My guess is that the doubled pins are probably added for several reasons, these could be:


mechanical stability (the mechanical stress, for example due to vibrations like when the device is used in a car, is shared between double the amount of pins).
redundancy, if a pin fails then nothing changes as the other pin is still making the connection.
maybe there are other devices that really need two pins to carry the current, that's not the case here (the currents are small) but the manufacturer choose to keep the same pin layout.
reasons we don't know.


In general it is "good practice" to just connect all the pins, as the pins that share the same connection are either next to each other or close to each other, this should not be an issue so I would just connect them all.