Split Heirs is a comic fantasy novel, from two authors reasonably well-known in that particular sub-field. While it is hardly a classic, it is fairly well-known among fans of this sort of book, and is quite well-plotted -- which is less common than it should be in comic SF/F.
The plot is very familiar; a kingdom is conquered by a vile barbarian, who takes the princess of the kingdom as his bride. It is hoped that their first child will be male, 'officially' binding the two royal dynasties into one, and making everyone a bit happier with the tense political situation. Unfortunately, the queen has triplets... and the barbarian tribe has a tradition that a multiple birth indicates multiple fathers. The queen quickly makes plans to have the two redundant children smuggled out of the palace, to live with their uncle, a Robin Hood-like figure who is mounting a resistance among the commoners.
Something goes wrong, however, and the two boy-children are taken, while the girl-child is left in the palace. And this error takes place just after the queen has announced that the child is indeed a boy. She quickly sends notice to the elderly nursemaid who had smuggled off the two children, but she has somehow disappeared without a trace, and the two infants with her. So the queen is left to raise her daughter in disguise as a boy, and the other two heirs are left for dead.
Eventually, the plot segues into a more complex version of The Prince and the Pauper, leading to a complex and sometimes somewhat crude comedy of errors. The story is complex, well-plotted, and enjoyable, and often hilarious.
Having said that, all too much of the humor of this novel is wedged into hackney banter and even more hackneyed stereotypes. One of the recurring jokes is the use of extensive and overly flowery prose to describe the generally crude and uninspiring events taking place; I personally find this annoying, and would much prefer a more direct telling of the tale. The authors also have a habit of joking about rape and bestiality, which is a pity, because I rather suspect that their target audience is not illiterate high-school students... Thankfully, there is a lot of redeeming content, although admittedly the bar for 'good content' in mass-market SF/F is pretty low.
While Split Heirs does not necessarily hold its own in comparison the masters of the comic SF genre, e.g. Terry Pratchett or even Robert Asprin, it is a highly enjoyable read. I would only recommend if if you do enjoy comic fantasy specifically, and not simply fantasy in general, but within that context, it is well-worth reading.