This is a great apartment. The rooms are small but well decorated, just as shown in the photos. It was very clean (and my wife has high standards for cleanliness). The apartment is located at the top of three flights of stairs, which might be difficult for very small kids (our youngest is 6, and he was fine).
It's very convenient to Istiklal street, which is just up the hill. Getting to the touristy areas of Sultanahmet is a (pleasant) 15 minute walk along Istiklal to a metro station, and then two train rides. There are bus stops a five minute walk away, from which you can get to lots of places in Istanbul.
Garen met us at the apartment, gave us a great orientation, and then left us to it. He was very responsive over email to the questions we had. He was an ideal host.