Singer

Maybe "court madrigal".

Just keep in mind if using "madrigal" that it's usually not used to describe a singer, but a type of song. Nothing wrong with using it differently, just best to be aware that people with certain musical backgrounds may misunderstand your meaning at first.

You also have the typical words - minstral (if they play and sing) or bard (if they write and sing) or troubadour (which I think carries more of a just singer context). Or you could always come up with a different and unique word. I think the most important part is for the word you choose to sound thematically similar to other titles you're using

Bard.

Or do they juggle and wear a funny hat?

Court Idol.

Minstrel?

Troubadour--not trabadour. Troubadours have a specific history of singing at medieval royal courts. Eleanor of Aquitaine had a very famous troubadour named Bernart de Ventadorn and the legend of Lancelot and Guinevere originated with troubadours and were thus included in the Arthurian legend. Troubadours also created the traditions of courtly love, thus popularizing the codes of chivalry epitomized by Richard the Lionhearted, Eleanor's son--who was considered something of a troubadour himself.