Yay! So far in the family we have Amanda from Little witch acadamia and 9s from Neir:automata as younger siblings, and Foggy nelson and Natasha Romanov from MCU. Oh, you also get Tatsuo and Matt as Derek's "adopted brothers"

I saw that Cullen did well in school. Maybe Cullen could have been that cool older brother who helped Derek with his homework when he was younger and helped Derek develop good study habits? Because, Derek is a pretty huge nerd.