How to remux:
My program of choice: MakeMKV
How to:
Import two sources
Choose which tracks you want -> Example:
Video: The best video track of the two
Audio: 7.1 dolby EN (source 1) and Stereo DE (source 2)
Subtitle: 2-4 subtitle tracks (if needed). 2 from source 1 in EN, 2 from source 2 in DE
Remux it into a MKV (basically a zip version of a movie folder with each track included)
Rename your own release to fit the naming scheme
Import into *arr/media library.

For an actual guide better search on YT/Google as only text might be difficult.