Hello Crispy
I am sorry if this response seems rather negative, but you suggested combination of car and loads raises my concern.
Even for a Sorento I think you may be asking rather a lot to carry both a roof box and cycles whilst towing.
I have seen a narrow roof box for skies, which might leave enough room along side to fit possibly two cycles on the roof, but the box would not carry much. Some cars and roof mounted bike racks can be too tall for ferries.
The other possibility of a tow ball mounted bike carrier has problems, as you have to add the weight of the bikes and rack to the nose weight of the caravan, and that combination must be within the tow bracket's capacity. Some ball mounted racks cannot be used when towing because the caravan my foul on the bikes.
If i were only towing in the UK my choice would be bikes on roof, and the other items destined for your roof box, stowed in the caravan.
Continental touring I would see if i could stow the bikes in the caravan with appropriate padding to protect furniture etc, and a roof box for other items.