[itsme]

This has been asked and discussed again and again in the forum.
The combination of several songs that you call a "set" in folk music is called a "medley" in other styles.
The way to go is to create one song in MobileSheets containing both tunes and naming it appropriately.
In your case you would have to create two of these combined songs, A+B for one band and B+C for the other band.
You can use the same PDFs if you add them on the Files tab of the song editor. To display both tunes on the same screen set Page Scaling Mode to Fit Width and Display Mode to Vertical Scrolling.
Having separate songs per band allows different annotations per band.