Are there really other selves at all

[anagogy]

So how much can we shift reality with our conscious mind, say if we're not all that powerful?

I hear that we are infinitely powerful. But I wonder behind the veil, how much can we shift the illusion?

Does everyone else have to agree on a reality we choose to accept?

The fact that our minds are divided while incarnate does provide a challenge to using the powers of the mind.  According to Ra using magic is a matter of using the unconscious mind consciously.  So learning to sway our subconscious minds is an important part of harnessing that creative power.  The subconscious is like the automatic part of your mind that ceaselessly performs repetitive actions of consciousness necessary for sustaining a given reality.

Everyone has to agree (that is to say, believe/accept at a subconscious level) if they want to inhabit a given reality.  Say one person leaves our reality and inhabits their own and no one here joins them.  We then label that person "crazy".  Or we label them as "in a coma", or "dead".  Now, that isn't their experience, but their departure from what we have accepted as reality has to be rationalized in some way.  Or sometimes you have people that temporarily diverge from consensus reality and they experience fantastical events involving aliens, cryptids, or an alternate reality.  They come back and again everyone labels them as crazy, or liars, or what have you, because it diverged from what the collective had agreed exists.  It doesn't mean their experience wasn't real, or the beings they experienced weren't real, but they are the only person from our reality who experienced it, so if they came back to this reality no one would agree that it was real.

So what you personally accept as reality is your own business.  And what other people accept as reality is their business.  When those vibrations overlap, to whatever extent, we call it "consensus reality", and proclaim it to be objective, when in truth, it is just two or more subjective realities overlapping.