yup! there's scene in ffx-2 that shows shuin being arested and the scene is in the first sphere that yuna got from kimahri(kimahri found a sphere that contains shuin and he thought he might be tidus so he give the sphere to yuna and there begins the sphere hunting...)

shuin is not tidus clone or original tidus... he is a guy from bevelle that looks like tidus and somehow i think he looks like in age around 20-25... as for lenne, she is a summoner and also a singer from zanarkand. both of them are real people from 1000 years ago... and of course its obvious that both of them are lovers... there's a war btw bevelle and zanarkand last time and i think lenne dont want to get involve in it so shuin wanted to use the forbidden machina, vegnagun to protect lenne... but lenne stop him and both of them got caught and got shoot to dead...

in the game you can get three different ending and one ultimate ending where tidus and yuna talk a little bit in zanarkand. u can get the ultimate ending by playing the game 2 times so that you will completed 100 % of the story...

and one thing about shuin being arested, i think when he atempts to use the vegnagun the first time, he got into jail and the second time is he escape from the jail and manage reach vegnagun but lenne stop him at that time... i thinks is like that lah...