As for the girl, her character's name was Ursula. I'm assuming she's the daughter of the landlord or the other guy in the apartment. But that's not a guarantee. She could just be someone living there. The landlord was Mr. Aziz and the other guy was Mr. Ditkovich (thank you, IMDb).
Ursula Aziz?
Ursula Ditkovich?
Dunno.
Black Cat's real name is Felicia Hardy with one alias being Felicity Harmon. Who knows. Both of those names could be assumed to hide her true identity. She's a cat burglar, after all. Why endanger her family?
Also, what's to stop them from completely altering Black Cat's background? She's not one of the better-known characters in the Spider-Man universe. They could get away with it. And the love triangle would be an interesting twist in a future movie.
As for a villain in S-M 3, I'm pulling for Venom. Don't bring the second coming of Green Goblin into the fold this early. Give him some time to develop his skills. The only downside to Brock as Venom in S-M 3 is that you have to find some way to explain the alien symbiote suit and have it meld with Brock very quickly to make him a viable villian within two and a half hours. Maybe it would be best to resort to Green Goblin II and get the ball rolling with Brock in the movie to set him up for S-M 4. Okay, guess I just contradicted the first couple sentences in this paragraph entirely. C'est la vie.