Campanula prefers full sun. And yes, you can plant tulips and daffodils in the same bed.
https://www.gardeningknowhow.com/ornamental/flowers/campanula/growing-campanula-bellflowers.htm
I also have one rose that has the same problem otherwise it is just the campanulas, it happenÅ› on old leaves, also on a prunus tree, Otherwise all good
That is usually an iron chlorosis issue. This article should help:
https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm