yes I was looking at that aspect when you posted -the top one will be anchored to a stud in the wall to the left via the handrail
the first one, closest to the wall it the one that is probably most easily to secure from below as it has lots of framing (2x4 underneat)
The middle one is not bad either -only the top one was questionable but I just realized it will secured on two directions so if I manage to anchor the bottom ones very well then it will be good
It will certainly be better than what is currently there
Not sure why they put the small spindle next to the post you can guess at the bottom right corner of this picture
That spindle is there for support. You think it looks odd but I guarantee it’s there for a reason.