True, Genoa and Pisa will probably have their King-tier titles. But I believe they said even ducal republics with coastal capital would generate their 5 families. My bet is that within another republic though, that won't happen - only one big election for the Serenissime Doge. But we're still left in the dark about how succession will work for lower burgher titles.
I hope that you can somehow influence who will inherit them, otherwise that would mean you couldn't keep any vassal or title or holding outside of your trade posts if you're no longer Head of the Republic, which would make the game less interesting IMHO.