Seems to me that the centre section of the camden bench is big enough for two - also, in one of the photos a lady is sat on the small side of the end section, so sharing a side is certainly possible - also, two people sat on opposite sides but at an angle could almost face each other, like a love seat?
http://cyan-teak-furniture.com/acatalog/garden_bench_gift_id...
A bigger problem I see is that such a bench is hard to position on a curb, next to a wall, etc, where both sides cannot be made accessible.