I recently started a game with the idea of getting both the thief and the cleric stronghold by dual-classing (thief11/cleric20) as I previously did with the famous kensai/mage. However in another thread Numinor said:
Though that is technically a bug, you are not supposed to have more than one stronghold.
You get whichever quest you do first, however the fighter and mage strongholds are bugged because they don't check if you already have a stronghold.
Is there any way of getting both strongholds? That was the main point for this character :-(
Install ease of use mod - multiple stronghold element.
With that you can get even stronghold not referring to your class.
Without mods there is no way.