What you’re looking to do is going to be complicated, but maybe I can help point you in the right direction.
As I understand it you’re currently keeping track of relationships between posts and terms in the terms. This would be better done with a taxonomy field in the post, which I think is the direction your heading in.
But you want to update the relationship fields in the terms as well, that’s the complicated part.
You’re going to need to create an acf/upate_value filter https://www.advancedcustomfields.com/resources/acfupdate_value/ for each taxonomy field and then update the fields on the term pages based on the taxonomy field https://www.advancedcustomfields.com/resources/acfupdate_value/
