Overall OP as many have said...depends on the school but still:
- 30 K housing
- School paid
- 42K monthly income
means roughly around 90K a month for the family (assuming ~ 8/9 k per kids for school)
It's OK, not in the top bracket but OK.
Make sure (you may have mentioned but I read quickly only):
- they also give you a flight back home every year (else that eats your budget)
- they provide good medical (some stuffs are super expensive here...yes a local system is good but dentists etc can cost you an arm and a leg for example).
As for housing, of course if you can increase it all the better but for 30K and depending on where is the school you can look at (and since you don't mind up to an hour commute):
- Ma Wan
- Gold Coast Area
- Discovery bay
- Some areas of Sha Tin and Ma On Shan
- Tsuen Kwan O
- Tung Chung / Tsing Yi
- Sai Kung / Clearwater bay if you are after the village style kinda thing
some other places I may forget -- point is pretty much everywhere in HK you will find areas that are close to some school and are "affordable" for your budget.
These are just some areas, there are more for sure.
For Example Ma Wan if you manage to get your Kids to ESF Tsing Yi and you work in central, it becomes a great place as commute will be short for all of you and living environment is great if you fancy a beach, a few resto and a nice pool. if you are into nightlife, fancy bars and high end entertainment it will be hell.
What I mean, is that you can do what you want in HK.