In searching for your previous threads in the Adobe Forums in order to answer another of your questions, I came across an April 2015 thread of yours that appears to have gone unanswered. Sorry about that.
Did you resolve this issue? If not, when you have time, we can go into this matter in more details.
It sounds like you were trying to achieve a split screen effect in Premiere Elements. Did you crop each to occupy 50% of the screen? There should not be any black borders if the cropping was done OK and the two parts positioned on screen. Please see
If you do want to pursue this matter, please supply more details including screenshot if you think that would help in the discussion.