I fully agree with pbirch. The rhythms are far more challenging than the range. The low D speaks well on an EEb as it's only an extra semitone of pipe away from our pedal C in the brass band world, and you don't have any long and loud versions of it, so the player won't run out of air. The high D is likely to be in range for anyone capable of playing the rhythms. I'd probably struggle on a first run through pitching the very last high D after the G# in tuba 1 as it's an awkward interval for me to imagine in my head, the top D has a note a tone away either side on the same valve, and the tuba 2 part isn't offering especially helpful clues on the harmonic front.