Tried to capture it all in the title.

My wife and I are flying to Denver on Oct 8 in CW (MFU). Strange as it may seem we want to sit together, but as I am Blue I can't pre-book seats without paying another £120. So I have been watching the seat map regularly, on the basis that if the amount of free seats got tight I would pay.

Anyway, up until about 2 weeks ago the flight was showing as a 3 class 777, and I had my eye on 5AB or 5JK (?). Then suddenly the map changed to a 4 class 777, but with the F section all blocked. Checking Expertflyer and no F seats are for sale on this flight.

So two questions -

Is it normal for BA to fly a 4 class 777 with F closed?

What seats would be best for my wife and I? 15A/B (J/K) would look best but I have only ever been in CW on a 747.

Apologies if these questions have already been answered elsewhere.