Also think about the aircraft rating. Hong Kong airlines and Dragonair both hiring, and both give you a rating, and both pay more than CX SO. You can use either of them for a rating, then move somewhere liveable.
The medical for your family is inadequate, and getting less adequate. Get a genuine quote for health insurance that is transferable back to your country of origin. Subtract that not insignificant amount from your SO salary.
Start googling English speaking schools and their fees. Ask them about debentures and places available. Is your wife able to home school your kids?
You can not understate the pollution issue. There is a phenomenal array of chemicals in the air and the water in Hong Kong. The Legco responsible for alerting you, is also the same group that would be liable if there was a problem ever admitted to, so you can see the potential conflict of interest there.
Just across the border, (Air doesn't respect borders), we have this tragedy unfolding.
An 8-Year-Old Girl Has Become China's Youngest Lung Cancer Patient - Business Insider Anecdotally, this record has already been broken. What price do you put on that?