1: The planets are indeed to scale within themselves, but the distances between the planets are not.
I do hope the planets aren't to scale, they'd have to be spherical shells built around planetary-mass black holes for that to be representative of anything vaguely approximating what Olympia is like in official 40k stuff, let alone anything habitable.
The Rock of Judgment is 20 pixels wide on my screen; if it's 200 kilometers across, that means 1 pixel = 10 km.
Olympia is 216 pixels wide on my screen, indicating it is ~2,160 kilometers in diameter. For reference, our Moon is ~3,745 kilometers in diameter, and Pluto is ~2,377 kilometers in diameter; I doubt this representation of Olympia is large enough to hold onto an atmosphere without highly esoteric terraforming technology. Also, if you want Earth-level surface gravity on Olympia, its average density is going to need to be ~32.47 g/cm3, or ~1.44 times denser than osmium, the densest element there is. Even if it's made entirely out of osmium, it's going to have ~0.693G surface gravity, and it's not possible for planets to be made entirely out of osmium.
Othreia is worse. It's 45 pixels wide on my screen, indicating it is 450 kilometers in diameter, but it's trying to squeeze ~84.59% of a Mercury (~4,880 km diameter, more than an order of magnitude wider) mass into something the size of Miranda): that is to say, so small that it's arguably incapable of being a sphere.
For reference, let's say you want Othreia to be something that could, hypothetically, exist naturally: a "cannonball" made entirely out of iron (how appropriate for the Iron Warriors!). 2.792 x 1023 kg (3.8x Moon mass) at 7,874 kg/m3 (density of pure iron) is a sphere approximately 4,076 kilometers in diameter (1.173x Moon diameter) with a surface gravity of about ~0.458G, both of which are consistent with a sub-Mercury sized body/mesoplanet. Giving the same full-iron treatment to Olympia with a target of 1G surface gravity gets you a mass of ~2.91 x 1024 kg (48.73% that of Earth) and a diameter of ~8,904 kilometers (69.88% that of Earth).
Of course, a planet cannot be made entirely out of iron, because other things will inevitably get mixed in over time, and the diameter and mass increase as less dense substances are introduced (gas giants are the logical conclusion of that trend). Still, these are pretty good absolutes for how small your planets could be while maintaining Earth-like conditions. If you're willing to skimp on gravity or introduce ultra-dense substances into their cores, you can make them smaller, but ~2.91 x 1024 kg in mass and ~8,904 kilometers wide is about the minimum size of a naturally occurring (i.e. densest component is iron) planet with 1G of surface gravity.
I think you just want the planets in OP to not be to scale, that's a lot saner and more explainable. Or you could just leave it as is, in the time-honored tradition of 40k writers making things believable and fun instead of realistic and having sane numbers.