I've read 10 chapters of this now and considering the slow releases I'll make a prediction as to how this will end. Maybe I'll look back on this in ~10 years when the manga will be at the halfway point.
Arnold will succeed in making Leo the emperor. However, by that point, Leo will no longer have any interest in the throne. Instead, he will convince Arnold into taking his place, for Arnold's sake. They will simply swap their identities. Leo will marry his maid, a commoner, something he could never have done as emperor. Arnold will end up with Finne and Elna. Because they are twins, only close family members would be able to tell them apart and by that point, any family members who are their enemies would have been eliminated.