We stayed at Josef's with our two children (9 and 11), and it worked well. They shared the bedroom and we slept on the fold out couch which was comfy. The flat is simply furnished but has the essentials, and Josef was very responsive to questions. The flat is in a quiet neighbourhood with local bakeries and a great pizza shop, and ten minutes or so walk to the more buzzing parts of Friedrichshain. It is convenient to transport and was a great base from which to explore Berlin!