Using cargo spaces for passengers is likewise rather dependent upon how the space is configured. The Atlas, for example, appears to be a massive container ship. If an Atlas always carries a full load of containers even if not all of them are full, then it may well be fairly easily usable as a passenger liner as long as the containers can be provided with a habitable environment, but if it does not, you're looking at a ship that doesn't have enclosed, protected spaces available for conversion - the 'cargo hold' is essentially just an open frame to which the cargo containers can be attached for the journey. A Buffalo, on the other hand, appears to be either a bulk carrier or a general cargo vessel with an enclosed hold; as long as the hold can be sealed enough to be habitable, it should be relatively easy to convert the cargo space for use as (fairly basic) passenger accommodations.
The impression I get from the Atlas and the Buffalo is that they're both of the same general design - a "spine" with a bridge at one end and an engine at the other, with cargo containers attached to the sides. I get the feeling that they're intended to use the same containers, too.
In the case of the Atlas, you have five rows of five (visible) containers, for (at least) twenty-five containers to a side. The Buffalo gets only two rows of one. The graphical differences I chalk up to "scale is deceptive" and "maybe the Buffalo's are welded in place and then painted over".
A better comparison might be to the
Hound; that's definitely got an internal bay, which could be more reasonably converted to pressurized passenger space than a corrugated metal box held on with a "magneto-gravitic coupling".