[Cerek the Barbaric]

If you are a fighter that duals to another class or a multi-class fighter/whatever character - you CAN get the strongholds associated with each class - so long as you do the De'Arnise Keep firstp.

Once you clear the Keep and go back outside, Nalia will initiate the dialogue that offers your the keep. One option is to simply tell her you need some time to consider the offer. During this period of time, simply complete the quest for the other keep, then return to Nalia and say "OK, I've thought it over and I've decided to accept your offer."

I don't know of any other stronghold that offers you the chance to delay your acceptance - so that is why you have to do De'Arnise first.

It's still much easier to just install Ease-of-Use Mod.