CCG vs Tax free child care

I'm going through the process of doing my student finance application for a SCITT course.
I will be 35 when i begin the course. I have 2 children my eldest will be 3 by the time i start the course and she will be going 5 days a week at preschool come September. My youngest is starting nursery 2-3 days a week in July he will be 11 months when i start the course.
I will be studying full time without any additional income. My wife isn't going back to her previous job after maternity, if she is working i imagine it will be part time in and around minimum wage.
She does have a trust fund which she gets about 5k a year from combined with part time work her total income was less than 20k for the last tax year. We will be taking money from savings and potential some small financial contribution from family.
I'm struggling to get my head around CCG and was wondering if i would be able to benefit from applying or whether i am better off just on the tax free childcare.
If CCG does workout better for my family what would i need to do regarding the current tax free childcare i receive for my eldest?