Well, I decided to heck with it - if I am feeling vulnerable/bullied/blind-sided, etc I need to do what makes me feel on better footing and if that makes me crazy or whatever so be it... I am sure I have that label anyway so who cares. I wrote back:
"Dear Teacher, I am sorry but I am really unprepared for this. I wish I had been given some notice of such a big conference. I was planning on attending the brief, standard parent-teacher conference with just you and I was not aware there were any major concerns. This, however, feels very sudden (as I am just the night before getting notice of this). DH can not attend tomorrow due to childcare issues and because he is recovering from surgery. I am uncomfortable going to such a big conference without DH, particularly when it seems quite outside the normal parent-teacher conference procedure. Is there some reason all of his teachers are going to be at this meeting? If so, I would like to be prepared for that. I would also like to have DH involved if this is more involved/complicated than the standard parent-teacher conference. Furthermore, I have a strong suspicion that, with all of those people present, it will take longer than the allotted time.
Anyway, perhaps we can reschedule when DH is able to attend, when I have blocked more time in my schedule and when I have some idea of what the issues are necessitating a meeting with all of his teachers. Again, I am very sorry but I feel a bit blind-sided by all of this."
I figure at the end of the day, I am entitled to have some notice about with whom I am meeting and why. It could be no big deal (e.g., this is just how they do it for atp/iep kids) or there could be "issues" - either way I am entitled to some notice, to be prepared and to have my DH there.
