the adventures of Cinny and company!
I have read every word you wrote and have so much to tell you! Your journey is really fascinating to observe and you will be so glad that you are documenting all this , especially those early videos. They will be fodder for humor someday. And pride as you see how the both of you progress.
Ok, when I watched the first video I was actually worried for you. If that horse had propped (suddenly stopped) or done a sudden dodge to one side, you would most certainly have gone off. Your seat was very insecure. Sorry. You were leaning way forward, popping out of the saddle, gripping with your knees, shoulders not square, and all that was a part of the total equation. Now, I also read about Cinny himself being out of balance, and I can see and understand that as also being a big part of the equation. However, You must improve you seat in order to help him. Sorry, but there is NO shortcut. So, lessons , lounge lessons on a schoolhorse will be invaluable. Your general openminded attitude and searching spirit are reallly admirable. They are the foundation, along with the boundless empathy you have for this creature. Now, you must build on it with the physical repition of learning to ride, better.
Now, to be more specific, after watching the video of one month later there is one specific and helpful critisim I can make. You have your feet well out in front of you in a bit of a "chair" seat and when you post, instead of carrying your own weight up and down from your own feet/stirrups, knees/thighs , you are kind of bouncing off his back. Well, not really bouncing, but you are requiring him to fully lift you. Since you are not lined up over your ankles, it is impossible for you to lift yourself in the post lightly. It means you are perpetually a tiny bit behind his motion and it forces him to work harder and quells his forward energy. (I know, vague horsey talk. Sorry)
So, one thing that will help will be a good dressage saddle that puts you in a good position lined up over your hips and ankles. Another thought I had, a chair seat is often a result of a saddle that is anged too far up in front/ down in back . I mean the horse might be very uphill . Or, the saddle is too far forward. OR, it is so narrow around the whithers are that it is propped up too high in front instead of lying along the whither/shoulder area nicely. In any case, it makes the center of the saddle, it's center of gravitey, too far back. Causes you to have your upper body too far forward and consequently, you are forced to have you lower leg forward also to offset the upper body.
Look at the saddle on him and see it the lowest point of the seat is in the middle, or if the saddle seems to be "climbing" his whither. If it is, use a small wedge (like a Cashel foam wedge) to lift the rear of the saddle .
This m;ight help.
What ever you do, when you are in the saddle, you need your hips over your ankles (shoulders over the whole shebang but you seemed to be reasonabley upright) in such a way that if your horse magically disappeared from under you, you would land standing on your little footsies and not your buttsies.
As for the sick baby, I feel for you mommy. Been there, done that.
Never forget that a horse, lovely as he is, is an animal and a child is your child. Never apologize for keeping one's priorities straight.
I really think you have a wonderful questing heart and It's a delight to read your posts.