Complex sentence: The present-day descendants of the Genoese settlers in Gibraltar are fully integrated as "Gibraltarians" and those with Genoese (and/or Italian) surnames make up almost 20% of the total population.
Split into simpler sentences: The present-day descendants of the Genoese settlers in Gibraltar are fully integrated as "Gibraltarians". Today, Gibraltarians with Genoese (and/or Italian) surnames make up almost 20% of the total population.