We arrived in HK last year and couldn't get our 2 boys into school for 5 months...nightmare believe me! I did get in touch with the education board and left a very long email letting them know that i was not happy with the situation and what could they do to help. The secretary of education in HK phoned me and told me that I would be breaking the law if i did not send the boys to school. Also informing me it was illegal to home school my boys and we could face a hefty fine.
Anyway, long story short...a lot of calls/emails back and fore, many heated conversations and the education board would still not let me home school, so we enrolled them in a local school until a place became available at an international school.
Lucky for us both our boys were accepted last September into a great school on the island, the local school was great for the short period of time they were there though.
Speaking with a friend yesterday who lives in DB, she informed me there were a number of vacancies within the school over there as a lot of children are leaving there to attend the new school openimg at Tuen Mun, The Harrow School.
Good luck with it all, things normally work out in the end, I hope you don't have too much trouble with finding a school 
Our boys were 5 and 9 when we arrived.
Also, schools will break up for the summer holidays next month and are usually closed for 8 weeks, I'd make enquiries now and explain your situation to the schools, some will be flexible for you with the applications.
Plus, a lot of children from DB go to school on HK Island. If you are flexible with where they go to school you may have a little more luck with getting them in somewhere. We live out at Tuen Mun and travel to Kennedy Town everyday, the boys and us are ok with this,
Good luck 