I mean, third-party OTAs can either charge whatever they want or whatever them and AC agreed to and that stuff usually isn't public.
With Expedia, I find that they're very by-the-book, and I was told once that they do have an AC rep on hand at the [AC] ticketing desk to explain some very niche issues with branded fares or guaranteed reservations to teach the OTA how to re-ticket/change some reservations, so these guys are comfortable with looking up AC documentation if you ask nicely. I hope then this is worth a phone call to find out! $50 a head is quite a savings if it's a full family


edit: sorry i ended up completely ignoring your reply and addressed nothing. i don't think this message is very useful to you anymore lol