We had a wonderful stay at Roumiana's house in Berlin. The property was large, well-equipped and very comfortable indeed. Our three kids were able to sleep in their own rooms and were very happy!
The S-Bahn and is less than 5 mins away and gets you into the centre of Berlin in about 15 mins, so we were able to enjoy plenty of visits into the city. There are supermarkets and shops nearby too, plus a brilliant open-air pool if the weather permits.
Communication with Roumiana was very easy, though we didn't really need anything. Highly recommended.