Pentax K-3 II has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Prime III processor. On the other hand, Pentax K-3 III has a
26.0MP APS-C (23 x 15.5 mm ) sized CMOS sensor and features PRIME V processor.
Another similarity between these two cameras is that both Pentax K-3 III and Pentax K-3 II sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the K-3 II and K-3 III sensor size comparison.
Pentax K-3 II and Pentax K-3 III have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.