Deed of Variation

My late father set up a discretionary nill-rate band trust under his Will with my mother and I as sole beneficiaries/trustees (estate to go to 3 charities if we were both deceased on my father's death). Now my mother wants my father's estate to come to me. It's only been 7 months since he died and I have obtained a Grant of Probate (GOP) under his existing Will (my mother reserved her right on the GOP). Do I need a Deed of Variation or can the estate come to me without needing to set up the trust?

For the Deed of Variation: will I need to get the permission of the 3 charities mentioned on my father's Will even though they do not profit from the Will?