My 2 sons (ages 10 and 12) and I stayed here at the end of February and we loved it! Xavi was an awesome, accommodating host. He arranged for a car to pick us up for our arrival and departure (around 30 euros), and he carried our (very heavy) bags up and down the narrow, winding steps to the apartment. And when we got into the apartment he spent a good amount of time telling us about the neighborhood (which is my favorite in all of Barcelona), and going over a map of the city with us. When it came time for us to leave, I had messed up the timing a bit and we weren't quite ready, but Xavi was super sweet and told me to take my time and he even helped me to throw the last things in our suitcases and zip them up. I don't know what we would have done without him!
The apartment itself is totally charming, and the deck is absolutely gorgeous. It would be so great to stay there in the summer months and have the chance to fully enjoy it.
My kids loved the 2 levels, and it was nice for me because I was able to escape for a bit from time-to-time. The loft is really a neat place for (older) kids to hang out and to sleep. The kitchen area is well-stocked (Xavi even left us orange juice and water and some wine for me!). The apartment is great for 2 or 3 people (maybe 4 if someone is okay with sleeping on the sofa).
I can't recommend Xavi's place highly enough!