Looking at the data sheet for the MAX14626 on page 5 it uses the phrase for pins 2,3,4 "Connect I.C. to GND" yet looking at the schematic for the reference design MAXREFDES61 where these devices are used the pins 2,3 & 4 remain unconnected.
Should the pins be connected to GND or be left unconnected?
The pins should indeed be connected to GND in your application. Both the part datasheet and the MAX14626EVKIT show this type of connection. Looking at the internal documentation for this part, these pins are used for test purposes. Leaving them floating could accidentally toggle the device into a test state. Please connect them to GND to avoid this possibility.