Complex sentence: FitzClare was the most popular captain in the garrison, steadfastly loyal to the Empress-yet de Soulis showed the men a document with his seal along with that of the other five captains, agreeing to surrender to the King.
Split into simpler sentences: FitzClare was the most popular captain in the garrison, steadfastly loyal to the Empress. De Soulis showed the men a document with his seal along with that of the other five captains, agreeing to surrender to the King.