I regularly attend both St John and the Maadi Community Church (MCC), which is much bigger in membership but has no building so use the outside area of the St John premises. The St John church is a small church (space for about 140 odd people). I am not familiar with the "church blessing" concept and how that will go down with an Anglican minister, but Reverend Paul Gordon-Chandler is the man, and I suspect you will need to speak to him to arrange. Good luck.