Confirmation Scotland (C1) and transfer of Nil Rate Band from predeceased spouse.

ETSL21

I am currently completing the C1 for my late Mum's Estate and we wish to make use of the full NRB which is available from my Dad - as her pre deceased spouse.  He passed June 2023. 
I have checked using the gov.uk website calculator and there is no tax to pay on mums estate.   It is an excepted estate.   At Q21 and Q22 of the C1 form I have ticked 'yes'.   Is that it as far as it goes in terms of claiming the unused NRB from my Dad's Estate?   
I have contacted HMRC and the Commissary at Glasgow Sheriff Court to seek guidance on this and each said it is the other that decides and to check with them so I am no further forward or clearer.  Some posters on here have said that they only filled in C1 ticking yes for Q21 and Q22 and it went through ok.  But I saw an other post that said they were contacted by HMRC and told to complete the IHT 400 for HMRC.

Wondered if anyone can confirm do I go ahead and submit the C1 and they will confirm if I need to do IHT forms thereafter.   

On the Inventory side of things I have a couple of items I am struggling with:

One is in relation to cash gifts mum made to her grandchildren at Christmas 2022.   How do I add these back into her Estate to show them on the inventory?

Another is the fact that as Executor of my Dads Will I still have inheritance that had not been passed over to my mum when she died.  So not sure how to show this on the inventory.   Do I list this a 'Cash - inheritance from predeceased Spouse held by Executor'.

I really would appreciate any guidance anyone can give me to get this completed, particularly as I have dropped the ball with it a good few times over the last 18 months and I know I need to claim the transfer of NRB within 2 years of Dad's death which was 30 June 2023.  So clock ticking for this now and I really need to get it done for my own peace of mind as much as anything else.

 TIA.