Add Team Members
When you add a new team member, just sending your old link will not work. You have to edit the team to add the new team members iCloud email address first, and then send them an updated link.
To do this, first go to Home -> Settings (gear icon) -> Team Sync Setting -> Manage Team on your iPhone or iPad. Team members cannot be added or removed from the Mac app. You team page should look something like this:
Press the Edit button, and then you will be able to type in the iCloud email address of the new team member.
Press the Done button (on the top-right) to save the email address, then press Update Team.
It will ask you to send an email to the new participant, so send them the link which will work on their device.
Remove Participant
To remove a participant, you can go to the same Manage Team page, then tap on the name of the contact you want to remove and then select "Remove Participant" from the options.