Your multi-hulls are extremely interesting and I think your designs are pretty much spot on. I also agree that a trimaran, though not as maneuverable as a twin-engined cat, could well do the job. Inherently, there is much to be said for three hulls as against two.
However, might I suggest that large billfish (in particular) are more commonly (and preferably) handled alongside a vessel, not athwartships across the transom. Two overriding concerns by a diligent crew who release their fish are (1) to keep the fish swimming into a flow of water thus ensuring an oxygenated supply of water, and (2) to keep the fish out of the props. When a large billfish is on the leader it can characteristically surge forwards, often in sympathy with the pull of leader. If at the back of the boat, this will often lead a fish into the props, particularly if the fish is aqua-planing with pectoral fins rigidly outstretched. Might I respectfully suggest a retractable steel-rung platform, as used on board tuna pole-boats, that can be lowered outboard alongside the stern sections of the hull in the closing stages of a battle with a fish ? It could do double duty as a boarding/dive platform and tender-berth at anchor.
