Though they’re rather small, that’s definitely Spirou and Fantasio (and Spip) on this 1959 cover. Or is it?
Today, Spirou and Fantasio use their original names in German. However, when they first appeared in 1958, as the title series of the comic magazine Der heitere Fridolin (“The Cheerful Fridolin”), they went by “Fridolin und Ferdinand”, and later they were known as “Pit und Pikkolo” (with Fantasio taking first billing for once). Interestingly, it seems like “Fridolin” (Spirou) got his name from the magazine, rather than the other way around, since the name had already been used for a German children’s magazine decades earlier, before Spirou was even created.
Der heitere Fridolin reprinted Franquin stories (this issue had part of Spirou et les héritiers, “Spirou and the Heirs”), along with Lucky Luke and other Dupuis series, but rarely used Franquin illustrations for its covers. Instead it used original illustrations that are, as a rule, shockingly poor. I thought this was a nice exception, but it turns out to be adapted from a 1957 Journal de Spirou cover by Will: