Are you saying this problem arises in all situations where multiple beings in multiple hypotheses make the same observations? That would suggest we can't update on evidence most of the time. I think I must be misunderstanding you. Subjectively indistinguishable beings arise in virtually all probabilistic reasoning. If there were only one hypothesis with one creature like you, then all would be certain.

The only interesting problem in anthropics I know of is whether to update on your own existence or not. I haven't heard a good argument for not (though I still have a few promising papers to read), so I am very interested if you have one. Will 'exploring their relationships' include this?