The setup I used when I get to max level (still only got there one time) was a level 10 Nicole (whatever color), a level 10 Adult Ruby Rose (red) (one level 10 Adult Mabel red would be better, but I cant get this stupid card), a level 8 Cerebella (blue) (I still wasn't able to upgrade it to level 10), and a level 10 Adult Ilulu (purple) (a upgraded purple Tifa Lockhart could do the same job. During the game, I would use only the doll with the Ruby Rose to get the balls, and control only the doll with the Nicole during the game. The doll with Nicole was a level 4 dog. The level of the dolls are also extremely important to get max level, because how strong their skills get at this level. If your dolls still aren't on level 4, you need to grind a little more :P