We are a family of 4 - with 2 children aged 12 and 16, and we stayed in Rebecca's accommodation for 2 nights. The apartment is lovely - very cosy, spotlessly clean and comfortable. I would highly recommend staying there. Rebecca was exellent at answering any queries so communication was fab too.
As other reviews have stated, the apartment is right beside 3 strip clubs, which is not ideal. However, it is about a 5 minute walk from the Grassmarket so a good location for our time spent in Edinburgh. Outside noise could be quite loud when in the living room but that is to be expected on any busy street in Edinburgh. The soundproofing in the bedrooms was good so we weren't bothered by the noise.
One thing to note, is that the parking is not at the location of the apartment but a few minutes walk away on another street. It isn't too far but may be an issue if you have lots of bags/young children/mobility issues - you can always park outside to load and unload if possible but not guaranteed.
Having said all of this we loved our stay - the apartment was perfect for us, and we really liked the roof area where you have beautiful views of the castle. We would definitely stay again.