Translation:I do not know how not to be afraid for them.
Earlier it was taught that “bát se” governs the genitive, it would thus be “jak se jich nebát”. Can it also govern a prepositional phrase with “o”?
You mixed up two meanings. Which is easy to do. Bát se jich = be afraid of them. They are vicious bad bad people. You should be afraid of them.
Bát se o ně = be afraid for them. You sent Gretchel and Hanzel to the forest for wood and they should have been back by now... Now you are worried.
Nevím, jak se o ně nebát.
I don't know how to not be afraid for them.
Nevím, jak se je nebát.
I don't know how to not be afraid of them.
That English translation is nonsensical. It literally would never be said by an English person - I can barely understand it.
Yes the english translation does seem a bit strange. Maybe it could have been "worried about them" rather than "afraid for them"