So it came to my mind that since the JD nerf, ships with more than 3500 cargo space can't use those. So the one thing is actually confuses me - can the bretonia liner use one of those?
The transports cargo limits for jump in group with JD IV is 3600 (The Serenity civilian transport) All others bigger than that cargo cannot jump together.
JD IV also allow to jump together with Battlecruisers or Cruisers, but not Battleships (too fat hehehe)
There is a page on wiki may help you a bit, if not outdated too much hehehe LINK