@gaboayala - Good to hear from you.
Within the Magic Link Plugin, we have the concept of Link Objects; which enable you to create Magic Links to address different requirements.
In your case, you will need to create a Link Object; which uses the User Group Updates Magic Link Type. Ensure the Support creating new items option is enabled.

From there, you will then need to assign the various users within your coalition, to the Link Object.

To manage the refreshing and sending out of Magic Links, see the Scheduling Documentation.
The coalition users will then be able to update any assigned groups; as well as creating new ones, from their respective Magic Links.

I hope this helps! 