I'm extremely inexperienced, so take what I say with a grain of salt.
I'm currently considering creating joining tables that contain three id's in them, and then writing my own logic on the model to make it work for my requirements.
By default, only the model keys will be present on the pivot object. If your pivot table contains extra attributes, you must specify them when defining the relationship:
hey, im encountering something similar. did anyone ever make any progress on it? im currently stuck between a custom 3way pivot model and table, or giving my many2many relationships in one table a true primary key to tie to another table to have many to many relationships on that as well