Thanks! 6.41 adresses the second question indeed!
I haven't been able to find a precise wording about the total strength that fires in a double hex, but from what I read in the rules, it seems a double hex is considered as a single "unit" so the total strength that fires probably always is the total strength of all undisrupted units (even if one of them couldn't fire due to the double symbol).
Your interpretation is correct. A two-hex position is still one position and if it fires, all undisrupted units fire.