Sarah Dagger

My Mother died in 2005. She left everything to my Father except £2300 to beneficiaries. The inheritance tax allowance then was £275000, does this mean that I would add this to the £325000 allowance for my Father, should he die or is it £325000 allowance from both parents ( ie £650000) now even though my Mother died 19 years ago? & is the £175000 Residence allowance added to this as well & if so how much & is it for both parents or just one? Ie total £1000000? Also any money given to any beneficiaries from the Wills, is this taken out of the allowance for my inheritance as well? How about if any money is left to charities? It would be so helpful to know this information. Thank you very much