Seek Plugin that maintains many:many relationship between 2 Entities

Hello, new developer trying to maintain M:M relationships in the above WP site.
? Website Registers two Person Entities (A & B) wishing to use site – Done
? A Registers an Initiative Entity (Food Van) seeking Volunteers – Done
? B signs-up as a Volunteer for A’s Initiative – Done
? A accepts B as a participating Volunteer for his Initiative – Done
? A seeks to know who are all the Volunteers for his Initiative – Cannot Do
? B seeks to know all the Initiatives he has signed up for – Cannot Do
? B also seeks to know who are all the other Volunteers signed-up on each Initiative he has signed up for – Cannot Do

To address the “Cannot Dos”, I seek a PlugIn that can maintain the M:M relationship between a Registered Person Entity and an Initiative Entity.

Just as Airbnb maintains the M:M relationship between a Registered Person Entity (Host & Guest) and a House Initiative?

Just as Uber maintains the M:M relationship between a Registered Person Entity (Owner & Driver) and a Car Initiative?

Or should I be seeking this type of help from another forum?