Multiple aspect ratio in one video

Hi, I have a very peculiar scenario. I recorded a play for friend - 3840 x 2160. Most of the action happens in the center stage while some scenes are extended beyond the center stage . Please refer to the attached pic. The Yellow dotted line shows the area (793 x 321) where most of the action happens - almost 2hours.

The red dotted lines shows the area (1339 x 321) which happens for around 10 to 12 times, each of 2-3 minutes duration. 

This is a one single video. 

Requesting help and guidance to process this in a way that when there is no action on the sides and only happening in the center stage, it should be in 793 x 321. When the action happens in the balcony area - it should strech to 1339 wide.

I have already done color and sharpness correction.

This is the first time I'm editing a video, hence it would be great if you can provide step by step guidance. Thank you so much!

Warm Regards

Sachin