If your aunt died in England, enter a search at the probate registry when you have her date of death to see whether she died intestate or with a will. It may well be that this company are referring to her if she died intestate. If you find out, you can then take up the cudgels yourself without needing to pay this family anything.
I disagree with Peter Pedant saying they are normally scams. The probate searching/genealogical industry is HUGE! They search the Times on a Tuesday where the Treasury Solicitor publishes the lists of bona vacantia estates (ie estates where people have died intestate and there appears to be no family so it will go to the Crown). These companies work 24/7 to trace the family trees of the deceased person and when they find a relative, contact him or her and say "we will give you all the details for a fee of 15%". Chances are the beneficiary would have no idea otherwise and the Crown would claim it. So whilst 15% can sometimes be a big whack, I take the view that it is better for the beneficiary to receive 85% than nothing!!