My husband and I used the self guided tour in the RS book and found that useful. Agree that private tour of the two are probably unneccesary, especially with audio guides as an option.
In regards to lines, we went to the Alcazar in the afternoon and waited about 30 minutes in line. Not bad but there's no shading and a teenage girl passed out from the heat right in front of us! You can also buy tickets here from the Alcazar (official site): https://oberonsaas.com/realalcazarsevilla/visitageneraldos
For the Cathedral, we didn't buy tickets in advance so we can have flexibility in our schedule. But the RS2016 book offered a really great tip to beat the lines. I just posted this on another thread:
When you're at the Seville Cathedral, make sure to follow Rick's advice of buying the combo ticket at the Church of the Savior a few blocks away, then literally walking past every one in line for the Cathedral to the area where tickets are sold. Just show your ticket to the security person there and they'll let you in. On the way, ignore all the dirty looks from the people waiting in the outrageous line.
That one tip was worth the cost of the book alone :)