“Fear of sin” is too interpretative to me, but I don’t know Pali.
I’ve read later texts that give the two terms the nuance of social vs. personal sense of wrong-doing. So, in one case you only feel bad because other people are shaming you. Maybe you didn’t actually do anything wrong, or maybe you just don’t get it. In the other case, you recognize something as having been a wrong thing to do, regardless of whether anyone knows about it.
It may be, though, that the two terms originally weren’t so well defined. In Chinese, the translation is for two synonyms for sense of shame & embarrassment. The positive form of shameless can be misconstrued as actually feeling shame, rather than just being capable of shame and thus being guided by that sense. That’s what the term really refers to in the sutras as a moral guide.
So, my translation is shame and conscience, or sense of shame and conscience to be more precise.