In other words - we did it! Pretty damn slowly but still quite shocked we did actually manage it. We took to the streets late last night after a bit of a discussion over route - it covers a few hundred yards more than week 3, and while the last couple of minutes of the final jog were pretty tiring for me both wife and I managed it!
I can't believe how far both of us, particularly wife, have come - not runners AT ALL and wife not much of a walker either and yet both of us are now putting in multiple minutes multiple times!
It certainly is a big leap from 3 but is still just about doable and it almost feels good to end up pretty close to our physical limits - though with enough steam left to walk back home fortunately!
Thanks everyone who reads and posts here because reading other people's experiences and getting their support has been really helpful and proved a great motivator and booster of confidence.