In the photo there are two anglers and two boatmen. The guide sits in the stern area the anchor, or bowman, sits in the bow to run the anchor for doing drops. The pictured set up is poled around. Other setups not pictured run the anchor rope to the stern area where the 'guide' can drop and pull anchor. With the square stern you can also use an outboard motor to get around.
It's usually a shared rod. Either way only one angler fishes at a time. The basic set up is to line the boat up to ensure the anglers are casting over the 'sweet' water (known holding lies really) and fish one or both sides of the boat while anchored. Start short and lengthen a bit between casts. 1 foot to 3 feet depending on what you are tying to accomplish. Once the limit of your casting is reached the boatman lifts anchor and drops you down to that limit allowing for some overlap between drops. If two are fishing you switch turns.
For everybody that is questioning...Mac and Gardener...these boats are VERY stable. There is no reason to sit and fish. Or learn a highwire balancing act. I get a lot of crap out here on the West Coast with my boat- all asking the same questions about stability and safety. I run a 15 horse prop and it motors along just fine. It's not going to win any races but it gets you there quick enough.
You hit it on the head: "one of the advantages of a boat is that the fisherman can be positioned so he doesn't need a long cast to cover the best water". That is why it is more of a nuisance to use a two hander. You are already standing on the fish with no need to cast any real distance. A single hander is more than adequate and really outshines a double for fishing such short distances. It took me quite a while to finally admit that as I plugged away spey casting with 13-15' rods.