ok.. how can you tell how many people have already claimed seats or which cabin is full or near full?

my main flight to Scotland is being booked through BA.com

i just couldn't find flight flight from edi to Kuopio through BA.com on one ticket thats why i went to the other site .... it seems for the most part every airline wanted me to go through Helinski then purchase another ticket...
(unless i was reading this stuff totally wrong)

but i was able to get it all one ticket through the discounted site