Wake up should not be hyphenated. "Wake-up" is an adjective as in a wake-up call -- a call to attention.
Can this not mean "Please wake brother up"? And what about "Please wake up, brother"?
"Please wake brother up", where the brother is the object, uses a different verb, -amsha.
Please wake brother up = Tafadhali amsha kaka! / Tafadhali mwamshe kaka!
"Please wake up, brother!" should be accepted because it's allowed us to change the word order with vocatives in the past to make it more natural, so it should here too.