"How can something be such and not be independent from some other such thing?"

Simply speaking, because suchness, or "state of being just as it is" is singular. There are not many "suchnesses". On independent existence and self-nature:

Nagarjuna’s critique of the notion of svabhāva (Mmk. ch.15) argues that anything which arises according to conditions, as all phenomena do, can have no inherent existence/nature; for what it is depends on what conditions it. (source)

Here is also an explanation as per Advaita but it's essentially just restating the same only in more detail (and with slightly different terminology):

https://youtu.be/Ftn4zCnheBk?t=1799

"us having animal minds (brains is another subject) is [...] mistake"

I could not find the article you mentioned. Anyway, we cannot talk about mind without talking about brain. If you ever had a dog or even a guinea pig, you could observe that these animals think, are quite emotional, and even dream. And science very much agrees. I have written about it previously so instead of repeating myself, I'll leave the links below.

https://senderspike.medium.com/heaven-on-earth-7d83596d4a0b

https://senderspike.medium.com/mind-brain-and-consciousness-9127f14dea4