"...with the other cities we would like to visit too, where in Germany should we concentrate our travels?"
I'm not sure what you're requesting here. Are you saying you want to visit places that are SIMILAR to London, Paris, and Vienna... or different? And knowing your interests would help...
The top sights in Germany from the list above are amusement parks... which do not interest me in the slightest. I tend to enjoy visiting new towns and smaller cities more than big ones that require subway rides (I'll spend plenty of time underground once I am gone!) or long inner-city bus rides. I am not a big foodie. I will eat and enjoy almost anything. I am not much for city bus tours at all, and I am persnickety about which museums I spend time in. I enjoy exploring these smaller places on foot, independently, using either walking guides that I have researched or created on my own. And I enjoy spending 1 or 2 days out of every week hitting some pleasant natural areas... mountains, river valleys, etc. I usually check to see if there are any local festivals where I am traveling - those can be fun.
Here is a link to selected day-trip guides from Earl Steinbicker's guidebooks. The list contains numerous places in Germany which I have visited (in the way I like to visit places) and enjoyed.
https://hastingshouse.typepad.com/hastings_house_us/2006/05/sample_daytrip_.html
So how would you describe the way you like to travel, the things you enjoy seeing/doing?