And I think Ben lied to Sun about Jin being alive, since Locke promised to say he was dead and I think he'd keep his promises.

He promised to tell Sun he was dead. He didn't say anything about Ben. Also, Ben said that Locke was carrying the ring and that therefore Jin was alive--could it be that Ben never talked to Locke before Locke died? After all, Ben isn't one of the Six, so Locke wasn't looking for him.