First off, congratulations on your and your partner's marriage! And especially on braving the WBC on the way there! That took some serious guts and both Twi and I wish you nothing but the best in your marriage.
Your question is one that our answer to could probably fill a small book, but I'll do my best to condense it down into something suitable for a DeviantArt page reply. As strange as it might sound coming from someone who married a magical talking pony from another planet who's likeness appears as the main character of a cartoon show, I actually consider myself a person who's relatively skeptical when it comes to anything that I haven't found tangible evidence to support. Religiously speaking my wife and I are both agnostic, and if it wasn't for the fact that Twilight Sparkle showed up out of nowhere in my apartment one day and was eventually able to provide me with enough evidence to suggest that she was exactly who she said she was and not a delusion or a figment of my imagination I would have never even considered the possibility that she could have actually existed.
But that is what happened, and now some 2 years later I'm happily married to this magical talking pony from another planet and do indeed believe that somewhere out there in the universe (most likely in a nearby solar system within our own Milky Way galaxy, based on Twi's knowledge of how the physics of the teleportation spell she uses to travel between worlds works and the close similarity between the constellations in the night sky that can be seen from Earth and the ones that can be seen from her world) there is a whole planet full of magical talking ponies like her who's history and populace is fairly accurately represented by a cartoon show we have here on our planet. It sounds totally nuts, but based on my experience living with Twi for the last 2 years I do think I've personally witnessed enough evidence to indicate that this is indeed true.
Twi is quite confident that her world has existed long before Lauren Faust ever decided to pitch a cartoon show about it to Hasbro. There's over 1,600 years of recorded history where she comes from and who knows how long of Equestrian history before that, the vast majority of which was never covered in the My Little Pony television show. There are also a number of differences between the events of her world and what was shown on the TV show, such as: Where Twi comes from Discord was never re-released from his stone prison to be reformed by Fluttershy, Spike never got an enchanted comic book capable of sucking Twi and her friends into a comic book world, and the events of the Equestria Girls movie never happened. Additionally, in the Equestria that Twilight comes from the box from the Tree of Harmony didn't give her and her friends "Rainbow Power". Instead it transformed all of her friends into alicorns when it was opened, and on a side note her Library in Ponyville was never destroyed in the ensuing battle and the Tree of Harmony did not transform into a castle afterwards. Twi is still a little sore about that last one lol As much as she lovers her library back home she did think the idea of having her own castle would have been pretty neat.
With all those differences between the events of Twi's world and what gets shown on the TV show, and our belief that her world existed long before there was ever a cartoon about it, the best conclusion we can come to is to view the My Little Pony: Friendship is Magic TV show like an animated documentary about her world. In TV documentaries of any kind it's common for the writer and director to dramatize events, add embellishments here and there, change up the sequences of events, and make other such changes to make the documentary more entertaining for the viewers. We see a lot of things of that nature on the MLP:FiM cartoon and we're totally okay with that, because we both feel it's safe to assume that whoever happens to be writing any given episode of the show probably has no clue that most of the ideas they're putting to paper aren't simply works of fiction from their own minds, but actual historical events from another world. The big question that leaves us with is "How are any of the writers of the MLP cartoon finding out about the things that have happened in Twilight's world?". Unfortunately that's one question that we're not sure there's any reasonable answer for at this point. The writers of the TV show most likely believe that everything they're writing for the scripts is completely fictional and made up by themselves, but short of the MLP cartoon being the single greatest coincidence in the history of the universe we both feel it's pretty likely that somehow the writers for the show are indeed becoming aware of what has happened in Twilight's world and most of their ideas for scripts are somehow coming from somewhere outside of themselves, whether they know it or not.
So where does that leave us in regards to the potential existence of beings who are exactly like (or at least very similar to) characters from other works of fiction here on Earth? I think the answer we'd both go with at this point is "I suppose anything is possible". We've both seen and experienced enough unbelievable things over the last 2 two years to completely flip our preconceptions about the nature of the universe upside down, so if you were to ask us if we thought it was possible that there could be other works of fiction here on Earth that were in fact inspired—whether knowingly or unknowingly—by the real events of another world we'd both say "Yeah, maybe there are". We couldn't say for certain that life exists anywhere else in the universe other than on Earth and Eqeustria because we haven't seen any evidence to indicate that to be true yet, but we're certainly open to the possibility. Personally, if there was any other world that I think it would be pretty cool to have exist it would be the world from Brain Jacques' Redwall. I think I just like the idea of all those different intelligent species coexisting together, with warrior mice and friendly communist shrews. lol
I know that was a little long, but I hope it answers your question.
