A double stroller is a real pest if you live on Hong Kong side. The footpaths are ridiculously narrow, and tend to not be flat (as it is mountainous). We have a bugaboo bee and more recently the city jogger (city select double). We also had a graco ultra light weight but my daughter HATED how rough the ride was so even though it only weighed <3kg and I could lift it on and off steps ect it had to go....
For 2 children, better to go with a bjorn and umbrella stroller (better as I have said but my daughter wont accept the ride) or bugaboo bee (but this is much heavier and a bit more inconvenient). For walking about on the streets this works best for 1 person. I seldom take public transport so am not sure how it would work, but for walking it seems to work pretty well.
The double stroller is downright dangerous when out walking on narrow pathways. It's heavy, has inertia ++++, and the last time I took it out, it tried to tip itself on the side onto the road with buses, taxis and the like zooming down. Will never do this again. EVER AGAIN. Felt terrible for putting my children at risk and for not being physically strong enough when my husband is not here to wheel my children out for 1 hour walks. Within malls the double stroller works really well. Within car parks, not so well. try to park strategically, so you don't have to weave between too many cars as the car parks are tight here, and most of the time you will have to do one big massive loop to get to the elevators. Forget about the bugaboo Donkey, this will not work in HK as beautiful as it is.
BTW if you are from the UK or states get your children's stuff there and ship here, much, much cheaper, stroller included.