Create 2-pass videos using ffmpeg & python

[olpdog]

My family (and a number of my friends) have come to me asking me to help them out with long term storage options for all their home videos. These are all digital videos and appear to all be in the h264 format (some mp4 & some mkv). The lengths of the videos vary from ~ 60mins to ~ 120mins. The files range in size from 2GB to 4GB. These are all home videos of family events, so there is no encryption to worry about. I suppose they could just purchase larger external hard drives, but some are too cheap to do so and some others really do not have the finances available to do so, so I would love to help them out. My plan is to compress the videos using 2-pass encoding so I can predict the approximate size of the final files (1GB-2GB each) yet keep them in the highest quality possible. I've created a couple batch files using ffmpeg to compress them, but from what I know about ffmpeg, there is no possible way to create a single 2-pass batch file, so I have 1 batch file for the 1st pass and another batch file for the 2nd pass. If it was just a few videos I'd do it manually, but, in this case, there are far too many to do it that way.
What I would like to do is create a single python file that will run both the batch files automatically. The goal is to have python open up batch file #1, and as soon as it completes the 1st pass, open up batch file #2 to finish off the video file's 2nd pass. Then repeat that pattern with each video file in the folder. I'm fairly comfortable with ffmpeg, but I'm just beginning to learn about python, so any assistance would be greatly appreciated. Also, if you know of a method to do this solely with a single ffmpeg batch file, that would be even better.
Thank you for your help!

I figured it out, flipped a pair of letters in my python file. Works great now