Multiple authors for an entry
We solved it like this... 

We created a Users field called “Article Authors”, for that Articles section. And there unlimited users could be selected as “Authors” of the entry (for search results, relatedTo, etc...). Each article typically multiple authors. 

But we assigned only 1 author as the only one with real editorial access, as the “owner”, so: basic Craft behavior. 

We thought this would be limiting, but actually it turns out, in practice, it’s pretty good to have only 1 person in-charge with end-responsability. It’s clear where it lies, and he/she will communicate with the team before changing things. This: in contrast with 5 authors being able to acccess and edit an article, which we thought would be a good plan, but in reality isn’t. This forces them to communication amongst themselves and it’s clear who’s responsible. 

Plus with the custom Users field, you basically maintain all functionality you want related to the entry. 

We have about 250 articles now running with over +1500 author members, and have not got any complaints.