Executor won't authorise any payments

[dunkertruck]

You stated your grandad's estate is worth a considerable amount.
If there is a delay in distributing assets after probate (which there appears to be in your case), the executors have a duty to invest money at the best possible interest rate for the benefit of the heirs.
When you get to view the statements of account check that interest has been added.

Very interesting, thanks for this. I have asked my Aunt to look into that.