If your team members have a red bullet next to their name it may be that they haven't synced or, at some point, stopped syncing their Salesforce account or their email account (or both!).
The best solution is to simply re-send them the invitation link and ask them to reactivate. Unfortunately only your colleagues can activate their accounts. You nor Thrive can’t activate on their behalf.
This is because their email provider and CRM need to get permission from them in order to connect and sync.