You should request a copy of the Grant of Probate and Will from the Probate Registry (you get them from the York Sub Registry, Duncombe Place, York with a cheque for �5 payable to HMPG). The front of the Grant will tell you what the estate was worth. However, if it was not a taxable estate, the figure on the front of the Grant will not be terribly accurate.
The Will will tell you who inherits what.
Only if you are a beneficiary can you take further steps.
However, you may have a claim under the Inheritance (Provision for Family and Dependants) Act 1975 as a child of the deceased, so it may be worth taking legal advice.