Cargo pod:
Modeled or only textured, there should be 12 seats, but each one may be less wide than a square (as per current Heracles model?). 4 seats could be integrated to the doors, indeed, and not displayed on the Battlescape model).
I guess that the mappers would spwan each inner UGV facing forwards at each front door.
As for the circulation inside the landed pod, it is currently possible with your (thin) model, but only at the rear doors (provided all the UGVs are spawned in the front half of the pod). It's better than with the Firebird anyways, and could be enough? It's true there are plenty of room inside the current in-game Heracles pod, but only one exit severely limits the tactical opportunities.
Carrier:
Last model features a cargo pod beneath the carrier. If possible, I'd have the cargo better embedded under/inside the carrier, perhaps half its height. This would lower the drag during flight (even if alien propulsion provides the required power). What happens if you just shift the pod upwards when it's attached to the carrier? I guess that the carrier's model should then be adjusted to hide those cargo parts that would emerge through it.
Also, the carrier's model could display a kind of VTOL capability, perhaps conventional thrusters? Or should we say that the pod itself hides those thrusters (unlikely)?
By the way:
Additionnal hardpoint for external 2x2 UGV could be featured on the rear of the carrier (or only textured), but the loaded UGV doesn't need to be modeled on the cargo+carrier models (in base, UFOpaedia and Geoscape models), of course.