I would create a custom post type to hold the bits and then use a repeater with a post object field. Alternately you could use a relationship without the repeater field because the selected related posts can be ordered.
Bidirectional relationships will not work for repeater sub fields. But they would work with a top level relationship field.
You would not be able to edit the text from both ends, the text would only be editable by editing the custom post type that holds the bits.
If is possible that you could make it editable on both sides using the post object field in a repeater, but would be complicated. You would have to add custom JS and detect the post object field was changed and then use AJAX to get and populate another field like a textarea. Then you would need to create an acf/save_post action that transfered the content back to the post holding the text to update the other end.
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