As others have said, the Azo will be fine.
As to the negatives, I'd try water first, but if that didn't work I'd try water with a little PhotoFlo or unscented dishsoap next before I tried fix. My reasoning is that the second might help the water creep between the negative and the envelope. My fear with fix is that it might react in some way with the envelopes (since we have no idea what they're made of). Before I soaked the whole mess in fix, I'd pour a bit of fix into a small container, tear off a piece of the envelope, submerge it, and wait a few minutes. If the envelope dissolves completely or if it stays completely intact, then I'd go for soaking in fix. If it becomes some sort of gummy mess, I don't think I'd try soaking the negatives in it for fear that you'd create something that you couldn't get off of the negatives.
If you do manage to free the negatives, a good wash, a good fix, and another good wash are probably all you'll need to do to them afterwards.
Good luck.