I agree with Mike about your first video. That's just timing and over-commitment by your uke. The notion of that being aiki falls apart when you have someone attack who can deliver power without committing themselves to "sitting in your chair". I don't think any of the people who are widely recognized as having aiki (Ueshiba, Takeda, Sagawa, etc). ever needed anyone to commit to giving them anything in order for them to feel their Aiki.
Your second video is getting somewhere, IMO. What you're doing there is not difficult for anyone to replicate. The questions are:
1. how much muscle are you using to maintain that structure?
2. how long can you maintain that against a hard push before even more muscles jump in to assist and likewise begin to fail?
3. Can you do that with a push from any direction?
4. Can you manifest that structure in an instant, from any direction?
5. Can you move while maintaining that structure against active resistance?
all while being relaxed, without relying on muscle to do things for you.
while there are a lot more things at work in Aiki than just skeletal structure, I think that if you take your example and add the five things above, you get closer to what aiki is and from that you can form a solid understanding of what it can do. I'm sure other people could add more things to it as well.
I didn't comment on your third video as I don't see it having any relevance to the discussion.