The Vevellis Chronicles

This is the story of two brothers Antonis and Nicola Vevellis set in the twilight years of the Byzantine Empire. Antonis is the son and heir while Nicola, was adopted by Andreas Vevellis as an orphan. From friendship as boys they grow into bitter rivals in love and ideology as young adults. They are taken under the guidance of Alexis Sartis, once a protégé of their Father, now a famous General, to be tutored in the arts of soldiering and letters.
When they meet Katarina the daughter of a Byzantine nobleman, Lord Virises, both are infatuated with her and compete for her affections, though at first this is playful rivalry. As they start to learn about the wider world around them, while studying in Constantinople, their ideological paths start to diverge; Antonis leaning towards the new power of the Ottomans and Nicola siding with his people.