All this makes sense, the thing I don't get is what is on Yong meanwhile.
Nothing... and Everything.
In first example she asks about her brother, why isn't he on yong, this is what she asks about and if he isn't then what is actually on Yong?
Allow me to answer your question another way.
1. If you ask about your neighbours dog wellbeing, what is the Self/Ti?
2. If you ask about your wealth luck for the year, what is the Other/Yong?
Unless it is needed for the information it provides, it is simply Nothing and Everything.
Now back to your question.
3. If we were asking about the brother, and we want to know if the brother would be in trouble. Would Other/Yong work? Would Sibling work?
4. If we were asking about the brothers feelings now they are in trouble. Would Other/Yong work? Would Sibling work?
5. If we were asking about the brother, and we want to know if they are in mortal danger. Would Other/Yong work? Would Sibling work?
5. If we want to know whether the brother still loved their wife now their life is certain to become forfeit. Would Other/Yong work? Would Sibling work?
You should see from these four questions, that there are subtle differences on what the Self/Ti and Other/Yong can encompass compared to the Six Relation representation, sometimes not even being needed. But does it mean they cannot be used in such a fashion?
Does it mean that the Six Relation (Sibling in this case) cannot also be used in the same fashion?
You will find that they both simultaneously represent the question at hand. But one or the other will yield a better way of showing you an answer, depending on what it is you are asking about.
For example. If you are asking about if your brother hates the wife you married last year...
Six Relations Sibling (your brother) always attacks Wealth (your wife) via Five Element theory (that is transposed onto the Six Relations).
So... What do you do here at this point?
I hope that helps.