Blimey! I didn't realise it was that pokey on board!! I though it was maybe a 1+1 seat layout with a small isle in the middle, so with those sort of bench seats, I assume there are doors at each row then, much like a slam door EMU??
As suggested by vlad above, each door gives access to two rows of seats. I think there are two doors each side, with those on the left staggered fore and aft from those on the right, so that four doors give access to sixteen seats.
You wouldn't want to be sitting next to someone too large, which I assume is another consideration at the seat assignment on the apron.
On my flight back, the pilot had been one of a group of Aurigny crew who'd been partying in the bar of the (now long gone) Butts hotel until quite late the previous evening. Work colleagues who lived in Jersey always referred to the airline as "the yellow peril"
[edit to add:] looking at Wikipedia, Aurigny has retired its Trislanders now, apparently replaced by Dornier / RUAG 228s, which have 1+1 seating but with an aisle.