Extreme solipsism is unlikely because I am here giving you an answer you don't want.
If you are God, then why would you make me up to bug you? Doesn't it seem you could find better ways of being disagreed with? I mean, I have a whole range of family relations and 'non-inlaws', etc. among whom I am immersed. And evidently you bothered to dream each of them up as back-story just so that when my character became relevant, I would be silly enough to be annoyed by your question.
If you are really alone, then why have you made things so hard for yourself, in two ways: 1) why is there so much detail that serves so little purpose? and 2) why do observe people acting as if you do not exist most of the time. And how can you possibly learn anything from either of these two things? But you have to admit that you do often learn from looking closer at seemingly meaningless detail, or from analyzing other minds.
If we are both aspects of something else, the 'real' single observer, then that is no longer extreme solipsism, it is basic idealism. You have admitted Plato's God, who is the outside basis for both of our realities.
To me, the most likely answer to the observer paradoxes in quantum mechanics is that only animals really experience time, because memory is a function of an exothermic mechanism, the brain. Real causation may have some other pattern, inconsistent with the second law of thermodynamics, while we cannot observe any state of being that does not follow that law, because we could never remember it. Time might go back and forth, retrying solutions until one obeys the laws of nature, locally or globally, failing over and over again, and we would never know, because only the last forward trace would be left without undoing in our memories.
This seems like a kind of like a biological-mechanism-level solipsism, but it is really the exact opposite: the 'weak anthropic principle'. It does not rule out other effects' reality, it just says that humans will not experience them, and their behavior does not have to make clear or consistent sense in the terms of the things that are basically biological, like time.