From the staff list page, if the person doesn't have a Last Login date set then they haven't accepted their invitation to join your account and set a password.
If they have never logged in before, simply click on their name to access that person's details page.
Once there, on the right-hand side, you'll see the option to click on Resend Invitation button.
Alternatively, you can simply email invitation link to your carers. You can access this link under Account --> Settings. Click on Copy to clipboard button as highlighted below and paste into email to your carers.