Hi CaliMom -
We were there a couple of weeks back and toured both sites. From what I could observe the guided tours were all external travel groups. The good news is the app comes free with your admission (itself not unreasonable in price, cheap in fact) just scan the QR codes inside/on the ticket.
Once downloaded it asks you to select language. There’s an audio guide which I listened to on my phone as I wandered round the Cathredral. I recognise that it would have been better through headphones (for everybody) but hadn’t brought any so I had my volume reduced and tried to find a quiet uncrowded spot to listen. However each guide, divided into several sections, also runs a type only version of the audio guide (bring your specs!) which is just fine which I used exclusively in the Capilla Real (it was very busy and I felt an inappropriate place to listen to the audio without headphones).
I found the Royal Chapel the more interesting, but the Cathedral is definitely worth seeing (they are separate sites) but I’ve always had a yen to visit the last resting places of Philipe The Beautiful and Juana The Mad! Plus Isabella and Ferdinand who are also buried there funded Columbus and also Isabella is the mother of Catherine of Aragon, who was the first wife of England’s Henry VIII (divorced!) so there’s a tie in to English history there too.
Personally I’m glad we visited both sites on our short stay in Granada, I would think if you are spending any time there it’s almost compulsory!
Hope you have a great trip!
Ian