The only schools that you can afford without dipping too heavily into your salary is ESF schools. From 2015 they will be putting on rather hefty non refundable "Debentures" (read bribes) to get your kid on the list. Expect to fork out at least $5000 USD per kid to get them on the list. This is the cheapest option in HK, so new hires, budget for this little addition upon your arrival. Check out the facts on the ESF website, you can google it as easily as I can, unless you are in China.
There are very few school slots available each year as teachers kids, past alumni, and kids with siblings already at the school get priority over your kids. There is hot competition for the remaining few slots. The other option is home schooling maybe, or the local system. Local is great if your kids are already fluent in Canto, completely useless to you if they aren't...
Did we also mention when you go to rent a place, the commission to the agent on signing is 1 months rent? Plus your bond of at least a months rent, plus a months rent in advance, so your 20k luxury pad just cost you at least 60K to sign. (About 10,000 USD you have to fork out, oh and utility bonds, and a few other little "gotchas"...)
If you take the job with CX or KA, it wouldn't be unreasonable to think that it will cost you about $20,000.00 USD for a wife and two very small kids.
"But mine are in KINDY!" you breathe a sigh of relief... Child education at KA doesnt cover kindy. A gentleman at work showed me the fees at a Lantau English Kindy, they were more than the fees at UCLA for a degree. Do your homework, Kindies know they have you over a barrel, and most of them are tied up with a school, so typically you have to go to a certain very expensive kindy to get a chance at the very rare school slots. Sound a little corruption to you too? Here in HK they call it 'business'.
Not trying to stir the pot here, all of these facts are checkable, just trying to assist your research.