Dark Wizard (quest questions)

So I'm playing this game and I have a couple questions regarding quests.

1) I got the Shinobi knife. I put it on a 4th class fighter (but it wouldn't let me equip it) and took them into the Shinobi Hamlet on a search mission. Nobody there will train my Knight or Ranger (I'm playing Robin) to be a Ninja. Can anybody think what I'm doing wrong?

2) There is a town where everybody has been turned to stone. Somebody tells you to go to this one town and ask about mermaids so you can help them. You go there, they tell you a sad story about a bard in love with a mermaid, he died, blah blah, and the mayor gave his harp to some other bard. The bard lost it in the moat. I found the harp, but can't seem to do crap with it. The other bard won't take it back. Nobody in that sea-town cares that you have the harp. I can't use it. Searching around that sea-town to try to talk to mermaids or something doesn't help? Can somebody give me an idea of what to do?