I have three heroes in this mission, and after talking to Raelag and Shadia, I can no longer play with them.

I had the same bug.
Before approaching Raelag, I dismissed all the secondary heroes. Only the three main heroes remained: a mage, an elf, and a knight.
Then I approached Raelag, and it worked: two heroes were added: Shadia and Raelag, whom I could now control.

However, I haven't completed the mission yet; I can't seem to defeat Isabel. Her army is too strong and grows quickly. I've fought with all the heroes, but none can cope. Paladins take out everyone very quickly. :mad: