I'm wondering if you mean that they were Christened CofE and now want to be confirmed in the Catholic church. If this is the case then talk to your Catholic priest or the priest involved with your school. They should be able to tell you what it entails and whether your sons can be confirmed. Nowadays, the Catholic church is very open and I'm sure they'd welcome your sons (or suggest a simple Catholic baptism first, if you are set on them being confirmed Catholic) - just have a chat with them or your son's teacher to find out a bit more.