How do I finish the edge where my deck meets the pool coping?

Scribe it, that's the normal way to handle a curved pool lip. Grab a scrap offcut of decking, drill a pencil hole through it a bit back from one end, and run it along the concrete with the pencil marking the board. The wobble in the curve doesn't matter at all becuase you're tracing it exactly, not trying to make a smooth arc. Leave a consistent gap of maybe 5 to 10mm between board and concrete so water can drain and the timber can move. If the gap looks uneven because the lip itself is wonky, that's the concrete's fault, not yours, and nobody will notice once it's done. On the ends question, cut them flush rather than leaving them hanging over the last joist. At a pool edge an overhang catches towels, feet and pool skimming gear, and exposed end grain sitting out in the wet is how you get split and rotten boards within a couple of seasons. Every cut end should get a decent coat of end grain sealer or at least a good slathering of the same oil you're finishing the deck with, especally spotted gum which loves to check and split on the ends.

What I did on mine was run a border board around the outside with mitred corners, and where it met the pool I ran a wide trim board following the scribed curve, fixed down over the tops of the cut board ends. It covers the saw cuts, tidies up any boards that aren't perfectly straight, and gives you a nice bullnosed edge to sit on at the poolside instead of raw cut ends. You can bend a thin trim board to a gentle curve, or cut it from a wider board using the same compass scribing trick. The border also lets you fudge the overall squareness a bit, because you rip the outer boards to suit rather than working to a fixed line. Slightly wonky edges disappear under a picture frame border, they don't disappear under an overhang, they just get moved further out where they're still visible. One last thing, if the deck boards run close to the pool coping, check the gap doesn't let small toes or a pool vacuum get jammed in there. Somewhere around a finger width is about right.

Did the same scribe job against a curved step on my last deck and the thing that saved me was a jigsaw with a fine cutting blade. The wobbly line looked scary untill I realised a steady hand follows pencil no matter how ugly it is. Cut a couple mm outside the line then snuck up on it with a block plane and some coarse paper wrapped around a paint stirrer. That raw saw edge on spotted gum will fuzz up and splinter if you leave it, so spending ten minutes softening it makes the gap against the concrete look deliberate instead of hacked.

Done a few pool decks back in the day and the scribe never lets you down. Before compass jigs and all that, we just used a flat pencil held against a offcut and dragged it along by feel. Same result. One thing I'd add on the fixings, if that trim board following the curve fights you, kerf the back of it with a stack of saw cuts a few mm deep and it'll bend like spaghetti. Glue and screw it down and you'd never know. Spotted gum is hard stuff on blades too, keep a spare fine blade handy or the second half of the cut will wander.