Yeah, I'm in the filming industry so of course I know Premiere Pro very well.
But personally I prefer After Effects because dope effects are there. It's where you can create lightning out of nothing!!!
Haha. I think you can just resize each video clip. Open both clips, then resize them. In the timeline, put both clips at the same timeline since you want both played at the same time. And then, just resize the clips at the main window. The window where you view the video. Man, it's hard to explain here cuz it's fucking practical, not theory.