Alhaitham is a serious man who values knowlege and wisdon, he can appear cold and uncaring, but that is not what he's like once you get to know him
Diluc is more quiet, stoic, cold. He does have a caring side, however, he's the most serious of everyone.
Ayato is more laid back. He's also the one who is a little more fancy and elegant but also kind
Zhongli is the oldest and wisest. He makes sure the group stays mostly out of trouble, tough he also does have a fun side.
~You're their little Prince