if you dual class from fighter to thief (or mage), can you have 2 strongholds? or you are having the stronghold of your first class?

Don't take my word for it, but I think that you keep the original stronghold, because I don't know. Just take my word for it. It would be one of those things they would have thought about when making the game.

Just the stronghold of your first class.

I'm not sure about dual-classing when you already have a stronghold.
IIRC you CAN have two strongholds if you are multi-class. This depends on the people you have to speak to. Nalia and Lavok for example offer you a stronghold even if you already have one, Renal Bloodscalp does not. So you could gain Thief and fighter stronghold, if you get Thief guild first

Originally, there was a bug in SoA that allowed dualclassed fighter kit/mages to start both stronghold quests, finisht the fighter one while still in the first profession, then get the second one as well after switching to a mage. Patches removed this.

I'm a fighter dualed to a theif, and I have the theif stronghold.

Before patching, I did dual a fighter/mage and take the sphere, then add the castle.

I currently am redoing the same class (my pc crashed and died before I could finish the game) and have the fighter stronghold. I'll let you know if I can get teh Spehere.

thief stronghold is enjoying?

I find the thief stronghold quit short. You only have to kill 1 traitor who claims to be a shadowmaster herself and she ambushses you when you are at the meeting in Waukeen's promenade. Do you remember the night knives? Now they wonna kill you but they are so weak you could kill them with both arms tighted. After that you have to say to your righthand what you will do with the moneystealing thief in your guild. Just stop their share in the money, after 5 days you will know you handled the right thing. This was everything but you also have to order your thieves what they have to do. At the first time i found this quit e cool but after a few times this get boring IMO

You still have to run the guild. My question is what happens when you're gone for prolonged times (which happens in the game)? Do you lose the guild for failing to make your obligations?