You said that if I change the past then it could affect other things like my sibling having never been born…but if I’m just changing my memory and not the actual past then why would that change things like that?
You can’t change the past. Taylor, in the video, made a point of saying that several times. Retroactive magic is a way to work with your memory of an event. That can change YOU and how you feel, but not reality. But “your memory is your imagination”, and you can change how you feel right now about wanting a sibling.
If there was a way to change the present to be in a version of the universe where you have a sibling, you’d have to
a) be into the idea that there we live in a multiverse where every choice spawns a new universe, and
b) find a way to move into a different universe where that event happened not just differently, but to your liking.
I’ve heard of people switching dimensions accidentally, such as the woman who woke up one day, to find she hadn’t split up with her abusive boyfreind, had a different job, and had made several other choices that were different than she knew. I assume she switched places with a version of herself that had a slightly different life. She still had the same company but hadn’t moved from her old flat etc. A lot was different. Here’s a version of her story - I don’t vouch for a word of it, but the concept in intriguing.
I’ve never heard of that being controlled or chosen though. It just highlights how hard this is. You can’t change this version because too many other strong spirits (ie other people, and we are ALL gods in our own right, asleep or not) are holding it the way they know it is, and you are not strong enough by yourself to affect all of them, AND create all the new memories for a brand new person that never existed before, AND persuade that new spirit to come and create all of that and be part of it. They also may have chosen to leave for their own reasons and not be willing to co-create this new reality anyway - did you ask them for thier permission to try, or their opinion at all yet?
There are other stories of people accidentally time travelling or universe hopping - another guy got off a plane with a passport for a country that doesn’t exist - but it’s always accidental and shocking to them, and then often they just disappear and no-one knows where they came from or where they go afterwards. It’s conspiracy theory-level type stuff.
I’m sorry, I really am, I lost my own twin when we were 3 months old and I still miss her - I totally see where you’re coming from - but I think your best best is to work on yourself and your energy in this matter to find your peace with it.