I have a 7×4 box trailer.
I have only fitted one bike in it but measuring the width of the bars, 2 bikes would fit side by side and the outside edge of the bars would be about level with the outside of the trailer wheels.
The only thing wih mine is it could be about 20mm longer as the tail gate hits on the back wheel and I have to bbow the side in to lock it in place. With it only being one bike that isn’t a problem but with 2 it would be harder to do as the wheels would touch closer to the outside edge.