Couple of questions
- Any preference house vs. apartment?
- Do you drive? Will you have a car?
- What's your budget?
Firstly, space is relative. Only 5% of HK housing stock is units over 1500 sq ft, and you pay a big premium above that. A typical HK house (known as a village house) is 3 floors of 700 sq ft each, but the measurements are weird, so it feels a lot less. Be prepared for less space than you had in the UK. Look for units advertised as "high efficiency" if you're looking at apartments.
That said, given that space is a priority and your DC are going to school in Kowloon, it's worth focusing your search over there because you get more sq footage for your $.
Clearwater bay/ Sai Kung have a lot of expats and are the "no brainer" locations to look at near Lam Tin. However, I wouldnt move there without a car, possibly two as very limited public transport/ none once you leave the main road. Houses go for around HK$60-250k per month depending on exact location, size and level of loveliness. There's a lot in the 60-80 range. However, manage your expectations- most village houses have very little in terms of garden, especially at the bottom of that range.
A less "obvious" area, but with an increasing number of expats is Shatin. This is cheaper and better connected by public transport. It's not close to the beaches. It's got some nice villa developments around it, but again you'd probably need a car.
Sorry cant be more help but I live in mid-levels (which is a possibility, depending on budget and school bus routes) so not that familiar with NT beyond those areas.