The processing of visas is a bureaucratic formality, with a succession of procedures that have to be gone through. INZ don't - can't - take any notice of how applicants are feeling. The officers simply have to follow the routine laid down for them.
Medicals are sent for assessment by machine. We think that there are probably key words that trigger referral to the MAs. The cases referred wait in a date-order queue to be looked at, and that is what takes time - normally, if there is a medical like your husband's where the person is actually fit and well, it won't take more than a few moments for the MA to see that, and send word to the CO that he has an Acceptable Standard of Health. I think your LIA is being a bit pessimistic about the timing, because 12 weeks' wait was when things were at their worst, just after mechanical sorting was introduced, and things have improved somewhat since then, so 8 weeks is about the timing at the moment.
I understand that this is not how you wanted things to be, but life is like that sometimes. There is nothing to be done about your husband's medical except to wait. Your course is going to start and you have to be there for that, whereas he can't travel until he gets his visa. Wishing you lots of courage to get on with things as they ARE. By the way, MAs can be very forceful about high BMIs, so it's possible that your husband's one will ask for it to be re-assessed. It would be a good idea for him to see a doctor or fitness trainer and start a regime to bring it down, so his intention and progress are documented.
Here
http://www.enz.org/forum/showthread.php?t=26174 is a LONG thread about one case where a lady had to reduce before the MA would pass her as ASH.