I am glad you had a good experience. Belgrano Day school also told someone I know that he couldn't enrol his (adopted) daughter the following year without considering that his wife had died 8 months before and that that was the last thing the girl needed. The man was shocked as he had attended...
The best bilingual school academically speaking is St Andrews. I don't know if it will be the best environment for your kids, though. Belgrano Day school is not as good as Northlands or St Catherine's but it could work.