I spoke to Nordonna about freeing her sons, but every time I go to the square in the caverns it just says "Empty manacles...", and when I go back to her, she simply says "please free my sons" (or something like that.

I've restarted the game, tried different combos of existing/new characters, but I'm stuck. Any suggestions, besides starting over?

Did you start the game using a brand new fresh ROSTER.DAT game? Freed NPC's stay free forever, and unfortunately, MM2 does not provide a way to "restart" a game, you need a backup if your original ROSTER.DAT file. Creating a new party does not reset NPC data , year data, or cartography data

If you restart the game, you can edit your new party to match the old one using Where Are We.

As for the specific problem, I don't know. Is it possible you freed them before completing the goblet quest? Maybe the game wasn't written to handle that? Are they available to hire in the inn?

I really have no idea what would help, but I guess I'm just kind of interested what state the game ended up in. The m manacles are in the northwest corner?