Pure chance that I saw this, I've just moved house and everything is chaos! But I'd plump for Paul, on the basis of "road to Damascus" moments.

Oddly enough among the few DVDs I've unpacked are "Enemy at the Door", which I'll have to re-watch! And also "Coriolanus" though mine is the 2010 version, which is very gory.

I hope the fic goes well! I have no doubts that you can do justice to their rather fraught relationship.