Qrew Legendimho, many to many is the way to go. If you try to shortcut it with multi select field, you will regret it later when it comes to various reporting issues.
If you have existing data, it's very easy to migrate that existing data to a many to many relationship. I can coach you through that if that's an issue.
If you wanted to make it quicker for your users to add the many to many child records, I could work with you one on one on a consulting basis for one hour to get a quick select method working, where you would launch off of a document and land on a list of potential people and then click click click on the various people and each click would add a child record and then a different click would take you back to the parent document record to see all those people added as people document records
