Hi Godwho is fitting them? if you can fit them surely you can measure them. I would possibly measure if i was supplying them.
I forgot you were in the Londonish area. He is looking for survey and supply, You may even be able to get the fitting as well he was just put off by a 4k fitting price for 7 windows from some local companys.
Its all pretty straight forward just some slightly awkward window sizes for fire egress and equal splits. 1740mm wide 3 pane windows etc, I had just warned him that under Fensa we can do it as long as we do not make matters worse but building control signing off may not be so lenient. Same for trickle vents