Update for anyone else in the same situation:
The emergency expedite process was comparatively straightforward. The person applying just goes I to US travel docs and hits "apply for expedite", upload documents and write a brief description of the situation. Both siblings' medical expedite appointments were approved within 24 hrs, and given about a week in which to schedule (although you could schedule out farther, you had to do the scheduling within a week). After the appt approval but before the appt I also had our state rep call the embassy. That was not helpful or a smooth process - they are used to calling for potential immigrants, not for B2 medical visas and I explained a LOT of times but still wasn't sure they understood the process-.
One visa was denied for no specific reason and the other was delayed (they kept the passport) while the sibling gets some legal documents together that require a judge and could take months which is longer than we currently have available, health-wise.
I'm pretty bummed about the denial -Mr. Daisy is not doing well at all- and also am hoping the getting-the-documents process somehow goes quickly.
I understand that there are NO immigration guarantees but am so frustrated to see so many people -even people we distantly know- walk across the border or abuse/overstay their B2 tourist visas having had that plan all along and then have free housing, food tickets, work etc with no immediate consequences. We try the legal way with stable 40+ yr old siblings who have traveled internationally, have good jobs and what the heck? Lots of disillusionment this week.
If anyone is A+ or O+ and is interested in kidney donation, please reach out! 😭