I only booked the holiday a week before, so completed the forms a few days before travel. I got the QR codes just after 10pm UK time, midnight Greek time. At that time it was a form each, now I believe you fill in one for each household, but that there has been confusion on the airlines' part about this. Any number of threads on TripAdvisor!
Manchester Airport is probably busier now than when we flew, judging by the planes going over our house now. Chania departing our Jet2 flight was the only one departing so we had the terminal to ourselves. The flight out was full, returning we had some empty seats around us. Jet2 handled it well. No queueing for toilets allowed, masks enforced, but allowed to take them off for food and drink of course. We took several cloth masks with us and changed them when we felt a bit uncomfortable. I actually found my chest felt a lot better for having worn a mask on the flight. The taxi back to Chania was on a very hot day and we had had a good meal, so our breath was hot! We checked in then went outside and took off our masks for a bit and put on a new one.
Take wipes and hand sanitiser and go for it! I was worried about the journey before we went, but it was fine.