Hi! You will move your whole family around the globe. You will need to spend a lot just for the move and to settle in.
As stated before, just signing a rental agreement will cost 3,5 monthly rent, which could cost HKD70,000.
Schooling is an issue, I doubt you can send your kids to local schools due to language and culture barrier, and international kindergartens and schools cost up to HKD15,000 / month (per child), Kindergarten being cheaper. This is just the tuition fees, add bus, food, trips, uniforms, etc.
Also, dont ignore random expenses, like going to Ocean Park, a few drinks in Wan Chai, beauty products for your wife, new television, christmas gifts, sudden trips back to UK because Grandma got sick, etc.
Leisure traveling is also expensive, as you always need to fly to get out.
Also, you need to save for your own retirement.
If you want to continue eating and living western standard, it will cost a lot. Cheese, cold cut, decent meat, milk, juice, etc is expensive.
You will be OK, but especially the first year will be costly, and I doubt you can save a lot.
If your wife can work as well, it will be a no-brainer.
Try to get a housing allowance, maybe HKD25,000. This will save a lot of headache.