We were 7, and Lucas' flat was perfect. Not easy to find a place where you can live with seven people in the center of London, with a big table, a nice kitchen and very nice bedding, at an affordable cost (for London...). Well, it is! The flat was also perfectly clean, and Lucas was extremely reactive, answering every questions within 5 minutes max. Every important place in London is at 30-45 mins from the flat with public transports, and is at a walking distance too.
Tl;dr: don't hesitate, it's a perfect place for a group/family of seven people (or 8 max)!