We loved Belén, Antón Y Joan’s place! It is in a great neighborhood (Russafa) that is lovely, lively and hip. This is a great base camp to explore the city and is a 20 min. walk to city center and far enough that it is not too busy. The flat is great and offers everything you need, we worked remotely for a week with 3 people and had no issues with the WiFi.
The building is beautiful and there are awesome historic windows/doors you can open up to really let a lot of sunshine in during the day and a nice breeze at night (in May). The only downside to this is you'll get some street noise during the weekends and nights due to the restaurants and lively atmosphere in the streets as they are not very soundproof. This was OK with me but would recommend to bring earplugs if you're a light sleeper. There are plenty of great restaurants and bars (and a craft beer bar) within a 5 min. walk.
Thank you again Belén, Antón Y Joan for this lovely experience we wish you all the best to you and your family!