I was in Lisbon for Web Summit 2018 with another colleague. The stay at Sofia's place could not have been any better. Sofia and her nephew Rodrigo were attentive and responsive from the first moment and we were treated exceptionally well. I would certainly recommend this apartment for any group up to 6.
You should be aware that the 2 bathrooms, which are superb, are essentially en suite to the two main bedrooms. Therefore, those occupying the 2 main bedrooms will have to expect that those staying in the 3rd bedroom or den will be 'visiting' when using the bathrooms.
The apartment was immaculately clean, fantastic location and quiet. Would stay here again for sure.