Nine is a masculine-presenting algebralian (any pronouns) with a late-90s skater personality: cocky, slang-using, self-absorbed, sensitive, sometimes whiny, and immature. 
Six is a feminine-presenting algebralian (she/they), irritable, intelligent, and leader-like; she can be aggressive and mean but deeply cares for others, especially Nine, and is an artist. 
Seven is an androgynous algebralian (he/they), social, music-loving, joking (but usually unfunny), and mature when situations turn serious