I think it still depends very much on the interview of the second child. I can only say that definitely SPCCPS is not the one that you have a higher chance. There are so many examples that the first child (or even the second child) got in but they subsequent child was rejected. (That also reflect that the family background alone is not the major issue.)
CKY - my friend's second child failed in the second interview. Since my friend's first child is studying in CKY, the school let the second child attend an interview again. The second child finally got an offer.