My family and I booked a private tour in January with Margarita Ortiz de Landazuri, who is recommended in the Rick Steves Spain book. She is responsive and easy to communicate with. Her email is [email protected] and here is the website: http://alhambratours.com/
We did Alhambra in the morning, then took a lunch break and met Margarita again for a tour of Granada sights. She was fantastic - best tour we've ever done!!