Had a great stay at Berk's apartment.
We had a bit of an odd check-in, since my in laws were checking in earlier than us. I was worried that it would be hard for them, since they are not so technologically proficient as to use vvhatsapp or airbnb app, but Berk managed to check them in with no problems whatsoever.
The apartment is located in an old building with odd holes in the walls, but as soon as you enter you are met with a really well renovated apartment with cozy furniture and layout. We were there in December, and it was kind of cold for my in laws when they just arrived. But then they turned the heating on and the apartment and all rooms immediately got nice and warm. (Theres also plenty of hot water for showers).
The location is great, just far enough away to be quiet at night, but just close enough that you only need to take a few steps to get to the vibrant streets of Kadiköy, where there are lots of shops and restaurants which are less touristy than on the european side.