The bad news: we seem to have mislaid our travel insurance and may have to ring up and ask for a duplicate.
The good news: Continental said the reservation for smallclanger has gone through, so they've taken my credit card details (again) and I've posted the incorrect ticket back in exchange for the correct ticket. Seats have apparently been reallocated so that we do indeed have a block of three on each flight.
Strangely, as of the close of business on 9 February, my credit card still hasn't been charged for the tickets we have already got. But then again, my Switch card also doesn't seem to have been charged for a cross-stitch pattern which arrived last week (or for last night's shopping, though that's more understandable).