RC or CAIS

my son and daughter are luckily accepted by CAIS and will join the school this Aug. However, I've just received RC's call and my son is offered a G1 seat, while my elder is still waiting for an interview.
I like CAIS for its smaller class size and Christainity, but like RC for IB (seems more well-known over Alberta in HK), and lower tuition fee. Another concern is my daughter is not offered a seat yet , not even an interview, and i do prefer them going to the same school. Should i take RC offer for my boy any opinion? thanks!