The sex is lighter in the TV series than in the book. The rape scene is pretty light, but they get the point across. There is no nudity so far.
The sex would be too much for regular network TV, but lighter than what you see in the Sopranos. I think it would be a light R. The violence is much lighter than what you got in Spartacus on Starz. They do show people getting stabbed. There is one scene where someone gets an ear cut off, but its not obscene.
I would screen it before showing it to kids. Its up to you. Lets put it this way, the sex is much lighter than what we will see on HBO in the GRRM series, but probably too detailed for network TV. The sex in the book was graphic, but it was important to the plot. The violence was necessary to get the point across that you are not in modern times and life was cheap back then.
The 3rd episode ends with the King coming to Kingsbridge to look at how the Cathedral is doing.
If your wife likes this book tell her to check out Cathedral by the Sea. It is much lighter on sex and violence. It takes place mainly in Barcelona during the late middle ages. It is a translation from spanish, but the translation is VERY good. The scope is not as epic as Pillars of the Earth, but very good too. They do a GREAT job of letting you know what it was like living in Barcelona in that time.
If you read the Amazon reviews people compare it to Pillars.