Thank you. I confronted her today. While in the end I got some answers and it seemed to clear some air between us, it wasn't pretty. It has been a while since I had a shouting match in German, but it always indicates that my mother actually listens. At least I hope that I got through to her.
As far as my brother is concerned, he's scheduled for surgery on the 15th of January and it stands unless his state would worsen severely. That's the most important thing. Whatever caused the aberration in his most recent results are (almost certainly, they are still looking into it) small potatoes compared to things that could 'disqualify' him. I'm talking about things like (acute) inflammation of the liver or increased intracranial pressure.
I still have to think it all over and sleep on it, but I figured that you (singular and plural alike) deserve an update.