Canucklass, not sure if this gives u comfort, but your child is entitled to be offered a place in the "Parish School". The difference between Congress and say Le Cheile/Irish Shcool is that the later 2 work on the first come first served basis and have no sibling policy, whereas Congress it is based on age & other siblings in school.
Dont want to offend anyone, but Congress Avenue gives me the creeps. Also i went to mixed schools all my life this is what i prefer.
Also i think children need to be baptised to go to Catholic School, i know i have to give copies on Baptism Certs.