How do I pin an instance of a sprite to another instance of the same sprite?

You have to add the sprite to a family so you can pick two instances independently

You need to add the sprite to a family. Then pick one instance of the sprite and another instance of the family and pin them together.

I suggest using hierarchies instead of Pin behavior. In the editor you can select both instances and add them to a hierarchy, no code required.

Great. Thank you very much, mates.