We are a family of 4 (10yr old, 12 yr old, and an adult with a mobility disability). We were about 5 minutes from 2 convenient metro/train locations. Sants station was great for getting to and from the airport, and Sagrada Familia and Placa del centre got us everywhere else. There were two grocery stores (with better prices) on our way to Placa del centre, but if you're not concerned about money or in a pinch there are 2 privately owned stores on either corner of the street. There's a pharmacy on the way to Placa del centre station as well. Prices in this neighborhood are significantly cheaper than around the tourist spots.
The host was wonderful. She sent us instructions, with video and pictures, on how to collect our keys, how to use the stove and wasing machine, how to get there from the airport (don't be afraid to take the train is crazy cheap and it will leave you so close to the apartment!). She came to meet us and explained some things in person as well.
The place was very clean, our kids took the twins in the bedroom and we took the couch bed. There's a.c. and heating so you'll be comfortable no matter when you're travelling to Barcelona. There are plenty of dishes, pots/pans, kitchen utensils to cook your own meals. There's a washing machine and drying rack (plus a laundromat super close by if you need to dry your clothes faster). There's an elevator which made life super easy for my husband. We didn't spend a lot of time in the apartment, but when we were there, we were all very comfortable.
I couldn't have asked for a better stay. This was truly a great experience!