shifting and schools in sydney (Sydney)

Hi,

We are planning to shift sydney in first week of july 13. Worried about school admissions and atmosphere in high schools there. Any guidence and suggestions from experience indiviual are welcome .My daughters are presently studing in grade 9 and 4, at CBSC school in Doha. We are looking schools in NSW area.
Studies at sydney high school (maths major) OR CBSC in India.I am confused.
Thank you all in advance.