Joint owners or tenants in common

[Pezza54]

I am not sure why you don't think the total RNRB on your mother's estate isn't £350k (2 x £175k)
RNRB wasn't around when your father died so he couldn't have used up any RNRB

[sodeflated]

Now that you mention that, I'm not too sure. I had filled out all the correct forms to use my mother's RNRB and also the form to transfer the RNRB from my father and put this info into the .gov RNRB calculator (I did this several times) and it said the amount of £300K. So I just assumed that was correct. I never had any queries from IHT people when the forms were submitted. It does seem a bit odd.

[sodeflated]

I've decided to go back through all the IHT forms I filled out and double-check that the information and figures I gave HMRC were correct.

Thank you for all the help that you've given me.