Dina - ENFP (Champion)
ENFPs like to change things for the better, and have contagious enthusiasm, but no patience for crossing I's and dotting T's. They are good at anticipating others' needs, but crave attention and recognition.
This one was pretty easy to place, I just took my own type and flipped the I to an E.
Nina - INFJ (Counselor)
INFJs are private, preferring one-on-one friendships to crowds, and often quiet about their own feelings. They are often thoughtful, artistic, and wise, and prefer to operate behind the scenes.
Nina is really hard to pin down because she doesn't quite fit into a stereotype. She's a shy, neat, serious, mildly grouchy, extremely energetic Romance Sim with fiery red hair. I see her shyness as being less about timidity and more just not wanting to talk unless there's something worth saying, and that she's a good listener. The grouchiness I interpret as a tendency to not sugar-coat things, though not to the point of being untactful. Those things seemed to fit the Counselor type the best.
Mike - ENFJ (Teacher)
ENFJs are good at making a lot of friends and facilitate community-building without even thinking about it; they act as a counter-balance to almost all social situations.
He's a popularity sim and an actual teacher, and I think "counter-balance" is a good descriptor for him.
Servo - ISFJ (Protector)
ISFJs are loyal, orderly and sensitive. They can be very shy around people they don't know, but are the sort of person who will always remember your birthday, and are never accidentally offensive.
This one was the easiest to classify. ISFJs even like to serve, so they say.
Don - ESFP (Perfomer)
ESFPs live in the moment, learn by doing, and enjoy promoting harmony and fun. This is a team player of the highest degree, but only if they aren't bored. They also enjoy their creature comforts.
He was a little harder to figure out because he's kind of a dual personality in my eyes, but I think it fits.
Cassandra - INTJ (Mastermind)
INTJs are analytical, pragmatic and logical, and are not scared to tell someone (or themselves) when they're being stupid. They emphasize efficiency, making them simultaneously loners and excellent leaders.
Morty - ENTP (Inventor)
ENTPs are clever and analytical, often with quick wits and a quicker tongue. They are very good at thinking outside the box, but (like ENFPs) are easily bored.
Pretty much exactly how I see him, and he actually is an inventor!
Bella - INTP (Architect)
INTPs are loners with a love of information and a knack for logic. This can lead to Sesquipedalian Loquaciousness, but also the opposite, as INTPs are best at describing complex ideas simply.
She's the hardest character for me to get a grasp of, so this was the hardest one to pick. I narrowed it down by looking at which type is most compatible with ENTP and then settled on this one. And she does do architecture in her spare time. ;P