Background Sound Issues on Session

I teach music online...with every student it's a challenge in setting up audio settings properly on Zoom to allow me to hear both student and THEIR Musical Instrument(guitar or piano). Sometimes this gets accomplished fairly easy w/ a few simple clicks...other times it becomes a nightmare ....and we get nowhere. A current student of mine just changed Computers (Windows format) ....and scheduled a lesson this past week ...but it never happened...Audio settings could not configured correctly to allow me to hear both Student & sound of Musical Instrument. ANY HELP??