[Cerek]

Working with the Shadow Thieves does present soemthing of a "moral dilemma" for good characters, but they are currently the best option in the game for those of good alignment.

There has been an extensive discussion on creating a Mod that does actually provide a "Good" alternative for the PC and party to get to Spellhold without working with the Thieve's Guild or Bodhi, but it hasn't gotten past the discussion stage yet.

As for the tasks required by Aran and Mae'var, there was a lengthy discussion about the specific encounter you mentioned and whether a good-aligned character could justify breaking into the home of Cowled Wizard and killing him just to please Edwin.

That discussion took place here --> Roleplaying/Alignment Dilemmas

Hope that helps.