There are sometimes kitchen boys, but unfortunately (for what you are looking for) they don't stay kitchen boys for long.
I actually read a story quite recently where the hero was a kitchen boy (by-blow of the King and a servant) but come the revolution he took on a more heroic role, and the other servants had either been killed, captured, or fled. The female lead was an apothecary/alchemist. There were some characters who were royal, but they were secondary, and the hero did not turn out to be the true heir or anything like that. It's called An Affair of Poisons. YA, if that matters to you.
Though there are kings and queens and princes and wizards in Patricia McKillip's Book of Atrix Wolfe quite a bit of the story takes place in the kitchens, with Saro who is a scullery maid, and of course the kitchen staff. McKillip often writes about characters who are musicians, and weavers, and scribes, etc. Even the Prince of Hed, in the riddle master trilogy, is basically a farmer.
But writers of books where all the main characters are servants, I can't think of any off the top of my head.