"The actors are with the architect on the stage."
Translation:Histriones cum architecto sunt in scaena.
About half of the Latin prepositions require the Ablative case (”cum” is one of them). The other half require the Accusative. And some, very few, the Genitive. In addition, there are prepositions that require the Ablative when they imply location, and the Accusative when they imply motion or relation, such as ”in”, ”sub”, and ”super”.
Well, super + acc would work for if they were "above the stage" (hanging from a rope to simulate flying? or maybe looking down) but super + abl can communicate "about, concerning." Prepositions are difficult in language acquisition. Keep an eye on how they work and you will get a feel for them with time.