These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Magnificent Bastard: Niccolo di Chimici. Silvia, the Duchessa of Belleza in book one, also qualifies as a female, protagonist version.
Narm: Sky's dad's stage name is Rainbow Warrior. And this man is supposed to be an American rock star.
I suspect this is a reference to the Greenpeace Ship of the same name, which was famously bombed by the French Intelligence Service. It caused quite an outrage, and has been referenced by a lot of real musicians.
He's explicitly stated to have been an '80s star, and considering Sky's probable year of birth, it would have been likely even so. It's still silly by modern standards, admittedly.
Tear Jerker: Lucien's Earth death in the first book - and the funeral - and Rodolfo's visit.
Luciano's brief reunion with his parents in City of Secrets.