Breakdown of Hasta mi hermano, que siempre está tranquilo, se pone nervioso en la entrevista.
Questions & Answers about Hasta mi hermano, que siempre está tranquilo, se pone nervioso en la entrevista.
Here hasta means even.
So Hasta mi hermano... means Even my brother...
It adds emphasis: the speaker is saying that if even this person reacts that way, then the situation must really affect people.
Compare:
- Mi hermano se pone nervioso. = My brother gets nervous.
- Hasta mi hermano se pone nervioso. = Even my brother gets nervous.
Because this is extra, descriptive information about mi hermano.
The part que siempre está tranquilo means who is always calm, and it works like a non-defining relative clause in English. It is not used to identify which brother; it just adds extra information about him.
So:
- mi hermano = the main noun
- que siempre está tranquilo = extra comment about him
That is why it is set off with commas.