I think that if anyone has a chance of portraying or living the normal life while being royalty it is William and Kate. They seem like the most humble and down to earth couple so it's safe to assume they'll be the same way as parents. While they will have problems being perfectly normal, I believe they'll do their best to give their children a life as normal as possible, with the few extra perks of course.
Yes, I believe that William and Kate will be able to replicate a modern family even though they are the royal couple, because they are down to earth. They have both spent a great deal of time around commoners. Even more importantly, they are committed to their child having a normal view of the world.
I think they are too far in the public eye to have a normal life. You can't think they will have a normal life, if they can't cross the street. They are royalty and by definition they are not normal people. The fact is they need to deal with it,cause a whole another generation, will be just as bad.
I do not think that William and Kate will be able to replicate a modern family. There are just way too many variable and scenarios that the family will face that will prevent them from being able to live normal lives. I think that they will be as normal of a family as one can be when the media is around.
The truth of the matter is that William and Kate live in a gigantic bubble. They cannot leave their bubble, and the world surly cannot get anywhere near it. So, if they have a family, the entire family will reside within the bubble and there's no way to circumvent that.