Complex sentence: Others with Calvagh were his son Con and Walter McSweeney who had brought two company's of gallowglasses of the McSweeney's of Fanad, also there was Donnell Gorm McSweeney and his followers who were the descendants of Donnell.
Split into simpler sentences: Others with Calvagh were his son Con and Walter McSweeney who had brought two companies of gallowglasses of the McSweeneys of Fanad. Also there was Donnell Gorm McSweeney and his followers who were the descendants of Donnell.