I think it's too complicated. There must be a way to describe the nature of the protagonist without including his mother. You didn't include her last time, so I'm guessing she's not that important. Also, I noticed you added clear antagonists, probably someone told you that your previous logline missed the real conflict. Okay, but how is this different? I think we have all guessed that the problem would probably be the other nations, who don't want them to rule, I mean that's the whole point of politics.
Let's take a break and analyze some other loglines in the period piece genre (I'm guessing your story is supposed to be one too):
(Braveheart) ''When his secret bride is executed for assaulting an English soldier who tried to rape her, Sir William Wallace begins a revolt against King Edward I of England.'' - The logline doesn't mention anything about the oppression of the Scottish or the politics in general. Instead it gives us a clear personal conflict, something we can all identify with. I have never led a revolt and I have never been oppressed to the point those Scottish were. But I did experience injustice and I did experience love, so I can already feel the emotional weight of the story.
Or here is another one, which is probably closer to your logline in style:
(Lawrence of Arabia) ''The story of T.E. Lawrence, the English officer who successfully united and led the diverse, often warring, Arab tribes during World War I in order to fight the Turks. '' - This one is a bit more objective. It doesn't explain anything about Lawrence's personality, but it gives us a clear image of the conflicts we can expect and why it's worth a watch. If it only said ''A young Englishman takes part in Wolrd War I against the Turks.'', we wouldn't care. But it already establishes the intriguing nature of tribal culture among the arabs, and gives the indication that we can expect it to be a lot more about internal conflicts than external.
Your logline doesn't really gives us personal stakes or an intresting twist. Why should we care that this prince is about to govern an empire? We don't know what a prince is like, we don't know if we care about his story. And the event itself doesn't seem too interesting either. I mean, okay, so some other nations oppose to their rule. That has only happened about 1 000 000 000 times in history.
Now what if you gave the prince a personal conflict? What if the prince and the princess were two entirely different people, forced into marriage and forced to rule together, despite having completely different views on what the empire should look like? What if the princess was against slavery, but the prince was for it? What if the prince was an atheist? I have never seen a movie about an ancient ruler who went against religion (probably because religious beliefs were a lot different back then, but it could be interesting to see).
If you don't want to make it that personal, you could still make the event seem more intriguing. Maybe it's not just the other nations who oppose to the prince, but his own servants too, because of his unconventional methods. Maybe it's not other nations, but the other side of Egypt which opposes him (I don't know when this is taking place, but there was a time when Egypt consisted of two parts, upper and lower). What if the princess was a foreigner from a nation that has just declared war on the country, and the prince would start to suspect her of being a spy?
There are so many ways to make the story sound interesting. And if you can't, then the problem is probably with the story. If the only thing you can say about it is that it's about two rulers, then what's the point? We can just watch a documentary about the pharaos.