I’ll try to simplify this.

Barbara dies and leaves her whole estate to David. Her estate is valued at £300,000. They are not related.

David dies a week after Barbara. David’s estate is worth £800,000 and leaves his whole estate to Jane.

Barbara’s estate will not pay IHT.

David will use all his £325,000 allowance with IHT due on the remainder.

Obviously Barbara’s estate will increase David’s £800,000 estate to £1,100,000.

Jane, is indirectly now the beneficiary of Barbara’s estate but she would like to do a deed of  variation for the full amount of £300,000 so that Barbara’s sister Alice gets all the money because once it goes into David’s estate IHT will be due.

Is there any way Jane can give Barbara’s whole estate to Alice BEFORE the late David inherits it. It’s so Alice gets more money.