Nice concept that fits in really well with the theme, a fun addition could be if the Quartett provided buffs or special abilities that were required to get through the next puzzle for example if one of them actually gave you the ability to shrink, which would be required in order to progress the level & then the next giving you the ability to Jump and so on. Adds a bit of functionality to them then once you have found them all you move onto a more complex level where you need to utilise all of the Quartetts abilities to complete it and get them Home to safety or wherever the story progresses to. Could be like pokemon meets platforming haha but yeah really nice concept, good job!