Question

Unlike his well behaved brother Alec was an impertinent child who constantly asked rude and intrusive questions of authority figures

Answer 1

Unlike his well behaved brother, Alec was an impertinent child who constantly asked rude and intrusive questions to authority figures.

(I'm not sure what you're asking here bud, so I just put it in grammatically correct terms. Good bless, buddy.)

Answer 2

Answer:

In this case, the context provides a clue by contrast with the underlined word. The word unlike suggests a contrast with well-behaved, implying the word impertinent means "ill-mannered."