Universal Credit Transitional Protection

Hi
My son received his migration letter for UC. He has his 6 year old daughter living with him and as its only been in the last year he hasn't been able to claim child tax credit as they no longer exist.
I've made a few online calculations with Turn2Us adding his daughter in the calculations.
He is receiving Income related ESA and severe and enhanced disability premium and PIP both elements enhanced.

Each Turn2Us calculation have shown a transitional amount.

Today we attended a CAB appointment and a very nice lady there told us that he might not receive much in the way of transitional protection as the DWP will add his daughter's child element into the claim making the difference between ESA and UC much less.
Is this correct?
Also am I correct in thinking there are 2 types of transitional protection? One for the guarantee you won't be any worse off under UC and one for the protection of the disability premium he receives?

Any advice would be appreciated.

Hi David
Thanks for your reply. The CAB person was aware that my son has never received CTC and this would be the first time he would apply. Would he still receive the transitional protection for his Disability premium?
Thanks

Another thought occurred to me.
Is it possible that he could add his daughter to the claim once his UC is up and running? Would he still receive and continue to receive his SDP transitional after that?
Thanks