Love that Elite 4 idea
Actually if you want to make their party, shouldn't they be like in games, mono typed?
The type could follow their personality and would follow the design you created or maybe inspire you with your design if you don't already have them all.
With the actual concept of Haruna i would think the type could be dark, fire or dragon? With the idea of a Tyranitar of somechineseguy it would probably be a dark type.
For Tomomi, I don't know. The cape make me think something like Ice or Psychic? Or maybe electric? Not really sure about this one. Actually the shirt could be the color of the type we choosen if we can decide one
For Rina, without concept i would say maybe Fairy, Water, or Normal? Have to be a cute type
And for Mami, since it would be the fourth one, dragon could be good. Other type that i think could be good for her would be Steel, Electric or Ghost maybe?
The idea of type that i give could not be good or the idea of assigning a type to them may not be good. If you love it maybe try finding the type you think would fit the best to one of the girls and maybe try to make a team around that type that could be strong with pokemon that could still follow their personnal style. (Actually when i say mono typed everyone understand that a ghost/steel can be considered in both type) Also possible to make one or two exeption in a team.
Also have to mention big Pokemon fan having every main version from emerald to X/Y