You can of course apply for EEA Family Permit from Spain and it will be much easier than getting one in Turkey because inside the EU, its relatively hassle free. You need to remember that your visa for Spain should be for at least 3 months. I don't know the exact length but the UK embassy will not accept your application if your visa for the EU member country you are in
( i.e. Spain in your case ), is valid only for a short term so I would advise you get a Spanish visa valid for at least three months to be on the safe side.

Good Luck