I use https://jsoneditoronline.org/, copy the contents of the save file into the site in code mode, then convert to tree mode.
The 'id' error is harmless and not related to your problems. Easily fixed by adding null checks to the person arguments of the addrelations function in globals.gd. These lines can be added to the start of the function using a decent text editor. Note, godot is very sensitive to the type of whitespace characters used, so even if it looks right you may break stuff. Lines have to start with the correct number of tabs and use the correct combination of newline characters.
if person == null || person2 == null: return
The 'remove_trait' error is mildly problematic, but again not related to your problems. That file has reversed the name of the function call man times; it should be 'trait_remove' instead.
