We were 4 adults and a baby.
It wasn't easy to find 2 bedrooms apartment in a reasonable price and I'm happy we fount Martina's flat. Martina was very nice and friendly before the booking and also after. The apartment is located in the best place in Prenzlauer Berg(!)- 5 minutes from the U-bahn Eberswalderstrasse and 2 minutes from Mauer Park.
BTW - it wasn't noisy at all(!) maybe because it was already a bit cold so we slept with the windows close but we were not bothered at all.
It is also located on the 1st floor which is amazing considering we had to carry a trolly up and down the stairs. Martina also provided us with a baby crib which was wonderful.
The only two disadvantages: there was no Wi-Fi when we were there and Martina told us she is working in order to fix it (we didn't notice that it was mentioned so it was our fault). The second thing is that for some reason it was a bit cold and the heating was not working consistently. It wasn't too cold in the city so we managed but still it was a beat annoying.
Anyway, I would still recommend anyone coming to Berlin to stay there!