I have run buck drivers in parallel before and tie the pwm pin to both drivers cutting the trace on the other driver so just one mcu controls both drivers. I have no idea if this can be done with the drivers above.
You would need to find a MCPCB that isolates both halves of the XHP70.2.
You might be able to parallel the switch on pin 3 of the MCU. Hard to say if the MCU’s will work properly joined together like that.
The other unknowns are if the two drivers pulling power off the same battery will trigger low voltage protection or just shut down due to all the electrical noise.
The hardest part will be finding a way to mount both drivers so they don’t overheat.
One of these days Shoki, Lexel or Lone Oceans will complete their boost driver. Until then finding a way to get some cells in series and using a buck driver is the best option.