No real spoilers here, I hope...
Duane paints the separation as
a) having happened in the immediate aftermath of an alien invasion (which both gave Vulcan space technology a steroid boost, and brought political matters on the planet to a boiling point)
b) taking place largely as an intellectual exercise, without mention of battles that are tearing the planet apart
c) not featuring any noticeable Surakian involvement on the side of the Sundered.
However, that need not actually contradict anything much, as the Duane telling of the events could simply be omitting a few irrelevant points such as the Surakian presence or the frankly quite everyday wars that must have accompanied the departure. In turn, The Sherman-Shwartz team might be omitting mention of the space pirate attack because it didn't directly touch the lives of the specific heroes of their story; with Vulcan as factionated as it used to be, half a dozen nations could wage interstellar war with space aliens while six dozen other nations would be fighting each other so intensely that they didn't even notice.
Also, Duane and S&S both list a number of events during the journey, and a number of ships partaking, but the details (such as ship names) vary. That, of course, is only to be expected: S&S are supposed to be giving the real story from a contemporary viewpoint, while Duane is giving the 2000-year-old legend from a 23rd century viewpoint.
Remus is of course a point of disagreement there. Duane describes the planet as somewhat more arid than Romulus, but still lush enough to be the "breadbasket" of the twin-world setup. S&S give no such quarter, instead establishing Remus as the fundamentally uninhabitable mining colony vital for the survival of the other, habitable but mineral-poor planet.
It's difficult to see how this could be reconciled. S&S might have taken a different tack, initially establishing Remus as habitable and then working in a terrible war where the planet is turned into a hellhole, but that option was not taken. Perhaps we could argue that Duane is using an euphemism when calling Remus "arid", and that the planet indeed did contribute key foodstuffs but only thanks to having endless supplies of geothermal energy by which to greenhouse-grow the plants. For a few centuries, it might indeed be that greenhouses on Remus would be the only viable way of feeding the population while crop after natural crop failed on Romulus. Or something.
Duane doesn't make specific mention of the distinct looks of the Remans, but then again, she seldom dwells on the skin color or even gender of her characters. It would actually well fit her style to politely omit mention of the fact that the Remans look like space vampires.