Depends really. If there was a lot of incest like here on earth it could be an issue. But if they're civilization is young enough, or fantasy magic or the divines just hand wave such issues away, there really isn't much worry for genetic mutations due to incest.
NGL, it honestly feels weird that that I typed out a similar response in another manga not long ago...
Okay, no offense to the mangaka/artist, but maybe it's just me, but the way those bandits in the last panel—or just adult men in this manga in general—are drawn looks off.
It's like they just slammed a tough-looking head on top of a toothpick-built body, kind of like a bobblehead, almost.