Related Questions:
Can you tell me why the double use is grey in my blocks?
Why can't I add different occupancy in my Group?
its not possible to put in the price for a double room is it any reason for this?
Answer:
This is due to the Mews integration, currently their availability block (i.e using Event Temple Groups) does not support occupancy-based pricing, so you are only able to use the 'single' column.
If you need to use Occupancy based pricing, it is recommended that you use Reservations instead