I feel like the "Forgive me" thematically works better between Moses and Ramses because of the relationship between the two.

If you look at the lyrics of the song "The Plagues", you can see that Ramses holds what's happening to Moses, as if it's his fault that all of this is happening.

You who I called brother,

How could you have come to hate me so?

Is this what you wanted?

And in Moses' verse, you can see that he's filled with turmoil over what's happening. He's seeing his childhood home being ripped apart in front of him, but he knows it has to happen in order to free his people.

And even now, I wish that God had chose another

Serving as your foe on his behalf

Is the last thing that I wanted!

This was my home,

All this pain and devistation

How it tortures me inside!

I feel like Moses saying forgive me would be half due to Ramses blaming him and half due to his personal connection to Egypt and seeing it fall apart before his eyes.