Residence Nil Rate Band and Taper of allowance

I am looking for clarification on how the taper provisions will apply where the first spouse dies after April 2017 with an estate under £2 million and the second spouse dies say in June 2018 with an estate of £2.4 million.

Does the taper apply to the two residence nil rate bands added together so that the estate has to be over £2.5 million for the benefit to be reduced to nil or would it cease to be of benefit if the survivor’s estate was anywhere over £2.25 million?

Sarah Pull
sas daniels