If you don't at this stage want to involve a solicitor for fear of racking up costs, the other body to contact would be the Probate Registrar. They can give general advice for free. The personal representatives of your late stepfather's estate would have had to apply to for probate to get their hands on the money in various accounts. The probate office is also where the lodged copy of the will be, once probate has been obtained.
This is where the probate registries ar in England & Wales.