No, I'm neither half of the Two Witnesses :=)
 
But seriously, the question of which half do they appear in is unanswerable. Scripture indicates they appear for the whole tribulation, once you understand how long the Tribulation literally is given as. To realize this it helps to know to read Bible prophecy literally like the rest of Scripture:
How To Understand Bible Prophecy Yourself For Sure
http://timmchyde.com/how-understand-bible-prophecy
Then read this for the scriptures that tell us the length of the Tribulation
http://www.escapeallthesethings.com/revelation-calendar-360-30-day-month-coming.htm