Both Olympus E-M5 and Olympus E-M10 III have 16.0 MP resolution sensors but Olympus E-M5's sensor is Four Thirds (17.3 x 13 mm ) and Olympus E-M10 III's sensor is Four Thirds (17.4 x 13 mm ).
Since Olympus E-M10 III's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus E-M5.
Below you can see the E-M5 and E-M10 III sensor size comparison.
Olympus E-M5 and Olympus E-M10 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.