Only your followers can view your activities when your account is set to private.
You can accept or decline anyone that requests to follow you when your account is set to private.
When you share an activity with someone that has the Relive app, but does not follow you on Relive, they will not be able to view your video in the Relive app. They will, however, be able to view the activity in a web browser, but they will not have access to your other videos unless you share your videos with them.
When you share an activity with someone that has the Relive app and they follow you on Relive, they will be able to view your video in the Relive app. They can also view the activity in a web browser.
When you share an activity with someone that does not have the Relive app, they will be able to view the activity in a web browser. They will not have access to your other videos unless you share your videos with them.

SHORTER DISTANCE than expected when recording on Relive

Why your activity distance might be shorter