The Winter Prince has some themes of incest -- necessarily so given a character like Morgause and the origins of Mordred/Medraut, but Wein also goes on to show how that kind of thing can really mess up the next generation psychologically -- realistically so, I think, but anyway the allusions are there.

There are also some pretty brutal (physical, non-sexual) things that happen to characters later on in the books, but they're carefully handled. And they're being marketed to a young YA audience, so my short answer would be yes. Anyone who's enjoyed the Attolia books will enjoy these, I think.