Translation:I do not know how not to be afraid for them.
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.
Because it means something different. https://forum.wordreference.com/threads/afraid-of-vs-afraid-for.2700609/
Do you have Google?
https://dictionary.cambridge.org/dictionary/english/afraid -- She was afraid for her children (= feared that they might be hurt).